do i need an invitation letter from China if i visit Shanghai/Beijing for 7 days on L visa?

If you don't have any sponsor in China, no need to provide the invitation letter, and you may provide the followings instead:
1. your travel itinerary in China
2. copies of confirmed return air ticket and hotel reservation bill.
3. Personal Written Statement (Covering Letter,with details as follows: A. name of the scenic spot; B. name, address and contact number of the inviting(contact company or person).
4. Certification letter from the working unit of the applicant(with details as follows: name and contact number of the working unit, the applicant's income statement or recent 6 months Bank Statement of the applicant).