Weather details are given below and these certainly play a part in deciding when to go, but a far bigger factor in your calculations should be the movement of domestic tourists. Three days paid vacation are given to workers for three major holidays in the year. The dates of these celebrations are carefully chosen so that workers in Chinese companies always have 7 continuous days of vacation time, known as the "Golden Week." These national holidays were first started by the government for China's National Day in 1999 and are primarily intended to help expand the domestic tourism market, improve the national standard of living, and allow people to make long-distance family visits. During the longer public holidays, Chinese tourists take to the road in the tens or even hundreds of millions, crowding all forms of transportation, booking out hotels, and turning even the quietest tourist sights into seas of humanity. In part as a result of these Golden Weeks, the number of domestic Chinese tourists has shot from 280 million in 1990 to a whopping 1.4 billion in 2006, the majority of these being peasants from rural areas. This should give you a clear idea of how crowded many of the "must-see" spots have become. Of course, if you really want to get a feel for the size of China's population, then this is a fine time to travel; otherwise give public holidays a miss.
China has three Golden Week holidays: the May Day holiday, the National Day holiday, and the Spring Festival holiday.
Peak Travel Seasons
Chinese New Year (Spring Festival): Like many Chinese festivals, this one operates on the lunar calendar. Solar equivalents for the next three years should be February 14, 2010, February 3, 2011, and January 23, 2012. The effects of this holiday are felt from 2 weeks before the date until 2 weeks after, when anyone who's away from home attempts to get back, including an estimated 150 million migrant workers. Although tens of thousands of extra bus and train services are added, tickets for land transport are very difficult to get, and can command high prices on the black market (official prices also rise on some routes, and on ferries between Hong Kong and the mainland). Air tickets are usually obtainable and may even still be discounted. In the few days immediately around the New Year, traffic on long-distance rail and bus services can be light, but local services may dry up altogether. Most tourist sights stay open, although some shut on the holiday itself or have limited opening hours.
Labor Day & National Day: In a policy known as "holiday economics," the May 1 and October 1 holidays were expanded to 7 days each (including one weekend). However, these so-called "Golden Weeks" were anything but, and resentment at everyone having to travel at the same time led to the shortening of the May holiday to 3 days in 2008. Regardless of duration, these two holidays mark the beginning and end of the domestic travel season, and the twin peaks of leisure travel, with the remainder of May, early June, and September also busy. Most Chinese avoid traveling in the summer except to cooler high ground or an offshore island, usually on a weekend. If you're traveling independently, and have the flexibility, it's best to arrive at a larger destination before the holiday starts, and move on in the middle or after the end. The disposable income to fund travel is more often found in larger cities, so these tend to become quieter, easier to get around, and less polluted. Noted tourist destinations around the country will be extremely busy, however. In Hong Kong and Macau, these are only 1- or 2-day holidays introduced in 1997 and 1999 respectively.
University Holidays: Exact term dates are rarely announced far in advance, but train tickets can be difficult to obtain as the student populace moves between home and college. Terms run for 18 weeks with 2 weeks of exams, from the beginning of September to just before Spring Festival, and from just after the Spring Festival to the end of June.
Local Difficulties: China's main international trade fair occupies the last 2 weeks of April and October, and drives up hotel prices in Guangzhou, where it's held, and as far away as Hong Kong. In the summer, pleasant temperatures in the Northeast (slightly cooler than the rest of China) draw students on summer vacation (which makes train tickets hard to acquire), as well as large Chinese tour groups; it may not be the best time for your visit. The northeast's Dalian is also overbooked during the International Fashion Festival in September. Across China, midweek travel is always better than weekend travel, particularly true at destinations easily tackled in a weekend, such as Wutai Shan and Pingyao. Already tight government-imposed travel restrictions in Tibet tend to increase around the Monlam Festival (sometime mid-Jan to mid-Feb), Saka Dawa Festival (mid-May to mid-June), and around the present Dalai Lama's birthday (July 6). The border crossing between Hong Kong and the mainland at Lo Wu can take a couple of hours at holiday periods.
China is the fourth-biggest country in the world, with the second-lowest inland depression (Turpan) and some of its highest peaks (Everest and K2 are both partly in China). Its far northeast shares the same weather patterns as Siberia, and its far southwest the same subtropical climate as northern Thailand.
In the north, early spring and late autumn are the best times to travel, both offering warm, dry days and cool, dry evenings. During March and April winds blow away the pollution but sometimes bring sand from the Gobi and topsoil from high ground to the northeast of Beijing, increasingly desiccated by the mismanagement of water resources. The sky can at times turn a vivid yellow.
In the south, November to February brings a welcome drop both in temperature and in all-pervasive humidity, although in Hong Kong all public interiors and many private houses are air-conditioned year-round. The southeast coast is subject to occasional typhoons from June to September which can close down shops, services, schools, offices, and transport for up to 48 hours.
Central China has some of the country's bitterest winters along with searing summer temperatures which give the Yangzi cities of Chongqing, Wuhan, and Nanjing their epithet "The Three Furnaces."
Tibet has springlike temperatures but a blisteringly close sun in the summer, while the dry winters are far milder than most people expect, at least in Lhasa. The northwest has perhaps the greatest range of temperatures, with severe summers and winters alike, but it is also largely dry.
Public holidays and their effects vary widely between mainland China and the two Special Administrative Regions, Hong Kong and Macau.
Mainland China -- A few years ago the Chinese were finally granted a 2-day weekend. Offices close, but stores, restaurants, post offices, transportation, sights and, in some areas, banks, all operate the same services 7 days a week. Most sights, shops, and restaurants are open on public holidays, but offices and anything government-related take as much time off as they can. Although China switched to the Gregorian calendar in 1911, some public holidays (and many festivals -- see below) are based on a lunar cycle, meaning their solar dates varying from year to year and precise dates often aren't given until the last minute. Holidays are New Year's Day (Jan 1), Spring Festival (Chinese New Year and the 2 days following it), Labor Day (May 1 plus up to 2 more weekdays and a weekend), National Day (Oct 1 plus up to 4 more weekdays and a weekend).
Hong Kong -- Saturday is officially a working day in Hong Kong, although many offices take the day off or only open for reduced hours. Weekend ferry sailings and other transport may vary, particularly on Sunday, when many smaller shops are closed and opening hours for attractions may also vary. Hong Kong gets many British holidays, traditional Chinese holidays, plus modern political ones added after 1997, but in shorter forms. Banks, schools, offices, and government departments are all closed on these dates, as are many museums: New Year's Day (Jan 1), Lunar New Year's Day (for the mainland Spring Festival, but in Hong Kong the day itself plus 2 more, and an extra Fri or Mon if 1 day falls on a Sun), Ching Ming Festival (Apr 5), Good Friday (usually early Apr, plus the following Sat and Easter Monday), Labor Day (May 1), Buddha's Birthday (1 day in May), Tuen Ng (Dragon Boat Festival, 1 day in June), Hong Kong SAR Establishment Day (July 1), Mid-Autumn Festival (1 day in Sept, usually moved to the nearest Fri or Mon to make a long weekend), National Day (Oct 1), Chung Yeung Festival (1 day in Oct), Christmas Day and Boxing Day (Dec 25, and the next weekday if the 26th is a Sat or Sun).
Macau -- Macau has the same holidays as Hong Kong except for SAR Establishment Day, but with the following variations: National Day is 2 days (Oct 1-2), All Souls' Day (Nov 2), Feast of the Immaculate Conception (Dec 8), Macau SAR Establishment Day (Dec 20), Winter Solstice (Dec 22), and Christmas Eve and Christmas Day (Dec 24-25).
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.