It depends on the places to visit, the type of weather you like.
Based on climate, most travelers would agree that the best time to visit Chinese middle and east part - China most popular tourist cities, such as Beijing , Xian, Shanghai , Guilin , Yangtze River cruise -- is May, early June, September and October.
The best season for Tibet and Silk Road tour: from April to October.
For Mongolia grassland, August to October is the best season .
If visit the ice and snow part of the country in Northwest, December to February is the best time .
Best time to visit Hainan Island : any time; it showcases spectacular tropical scenery year around .