Any foreign visitors wishing to enter China must have a valid passport and obtain a China visa before coming. However, people of some countries who want to visit China temporarily are permitted to enter without a visa according to visa-exemption agreements, or in accordance with principles reciprocity of national interest.
If you require an invitation letter for visa purposes, please contact Prof. Jianqiu Xu (Email: jianqiu@nuaa.edu.cn)
Please check out here: https://cs.mfa.gov.cn/wgrlh/lhqz/lhqzjjs/