You can submit the following documents to China embassy in Katmandu in person or entrust someone else to submit it on your behalf:
1. The original passport with at least six-month validity and two blank visa pages
2. Truly completed and signed Visa Application Form of the People's Republic of China
3. One recent passport-photo size color photograph of the applicant.
4. Invitation letter (if visit for the first time).
5. Proof of relationship, photocopy of the identity document and household registration of your Chinese wife in China.
6. Other additional documents required according to the merits of each applicant, e.g. bank statements, round-trip air tickets booking, etc.

Usually, it takes four working days to issue the visa. If the visa is needed earlier, additional urgent fee will be charged.