Can I get 45 days visa for medical treatment in Chnagsha, China

Yes, so just submit your application with the invitation letter. Other documents required:
1. Application Form with a recently-taken color photo glued to or stapled on.
2. Valid passport and a copy of information page.
3. Personal written statement (covering letter with details as follows: place to visit, name, address and contact number of the inviting / contact company or person).