In the northern part of the country, that is, Beijing, Dalian and Xi’an, it is better to come from March to May or from September to November.
You will find flowering and escape from the humid summer heat. In winter in this region from -2 to +5 ° C, but there is a strong wind.
In the central part of China — from Shanghai and to the south — there is no centralized heating. From October to April, the houses are damp and cold. The Chinese walk at home in outerwear and heat their homes with air conditioners in heating mode. I was in Shanghai at the beginning of October and slept under the warmest blanket. In summer, it is just as humid and stuffy there as in other parts of China. I advise you to come to Shanghai in May or September.
It is always hot in the south: even in February in Shenzhen up to +20 °C, and in summer — up to +35 °C. You can squeeze a T-shirt every half hour. On Hainan Island, summer is all year round, but in winter the water is invigorating — usually around +19 °C. If you are planning a beach holiday, it is better to come here from March to November.
I do not advise you to plan a trip to China on the Day of the Formation of the People’s Republic of China, from October 1 to October 7, and for the period of the Chinese New Year, in late January — early February. At this time there are a lot of tourists and overpriced prices for everything.