There will be two kind of invitation letter, please choose which kind of invitation letter you need.
1) Invitation letter for VISA application
This type of invitation letter is issued and stamped by the Foreign Affairs Office, this may take around 10 working days.
2) Invitation letter for travel proof
This type of invitation letter can only be used for Chinese VISA-free participate, which is issued by the Foreign Affairs Office of IMP. These kind of invitation letter takes about 2-3 days, and it can be used as your travel proof
If you have special needs for the visa invitation letter, please send your request and the information to y.p.zhang@impcas.ac.cn.