China is just a vast country of course that it encompasses several different climatic zones and it is impossible to generalise about the climate in China. Regional variations in climate are complicated by micro-climatic factors such as altitude and geography.
In winter most areas become cold and dry, in summer hot and rainy. Extremes of cold are reached in the deserts and the Himalayas whilst cities along the central Yangtze River aren’t known as the 3 furnaces for no reason. In the far south things get tropical into Yunnan and Guangdong.
Generally speaking spring and autumn are good times to visit the main sites and cities of China. Winter can see snow and freezing temperatures in Beijing whilst temperatures in the 40’s in Central China are not uncommon in July and August.
The Southwest coastal area including Hong Kong can be affected by monsoons, usually in August and September. From April and May, the rainy season monsoon reaches the southern provinces of Guangdong, Guangxi, and Hainan.
In June, Southern China gets more rainfall, known as plum-rain weather, coinciding with the ripening of the plums. Northern China sees the influence of the monsoon rain from July and August.
By October the monsoon influence has usually subsided.