China's climate varies from bitter cold in winter to unbearable heat in summer.
The Yangtze River serves as China's official dividing line between north and south. Given the size and varied landscape of the country, there is no one time in the year when weather is ideal in every part of China. Of course, the warmest areas in winter are to be found in the South and Southwest, such as Sichuan, Banna in Yunnan, and Hainan Island. In summer the coolest spots are in the far northeast.
China has a climate dominated by dry seasons and wet monsoons, which leads to clear temperature differences in winter and summer. In winter, northern winds coming from high latitude areas are cold and dry; in summer, southern winds from sea areas at lower latitude are warm and moist.
China climates differ from region to region because of the country's extensive and complex topography. In the south of the Nanling Mountains, rains are prolific and the temperature is high all year round. In the Yangtze and Huaihe river valleys in the central part of China, there are four distinctive seasons.
In northeast China, summer is short but there is much sunshine, while winter is long and cold. Precipitation is limited in northwest China where it is cold in winter and hot in summer. In southwest China of low latitudes, the land is elevated high, and has characteristically vertical seasonal zones.
参考资料：http://www.china-travel-tour-guide.com/about-china/climate.shtml