What should i wear for china trip next week on 18th march? and how about the weather?

Well, it depends on where you go. If you go to cities in the southern area, such as Guangzhou, Xiamen, or Shenzhen, you can a thin coat, jeans as well as summer clothes, because it is already very warm there. If you are going to the northern area, such as Beijing, Zhengzhou or Xian, you still need to bring some warm clothes with you, such as thick coat and sweaters, because that the temp difference in northern cities are very big in spring period. It would be sunny or clloudy in most of the cities recently.