China lies mainly in the temperate and subtropical zones. Generally, its southern part (East China, South China and Southwest china) is warm, humid, and rainy; its northern part (North China, Northeast China, and northwest China) is dry and windy.
In spring (March to May) and autumn (September to November) you will need a lined jacket or woolen sweater over light clothes. In summer (June to August) cool cotton garments are recommended. In winter (December to February) a light cotton-patted coat will keep you warm enough in the south; but in the north a heavy woolen coat or down parka is a must.
Later spring and late summer are often rainy especially in the southern part of China, so you would be wise to bring some rainwear with you. And of course good walking shoes are essential at any time of year.