Mrs.poonam, do you mean you want to know how many months your parents can stay in China? Unless specifically requested by the applicant in his or her completed application form and approved by consular officers, a single-entry visa is valid for 3 months, and a double-entry visa valid for 6 months, both with a 30-day duration of stay.

Your parents can apply for single-entry visa with 3 months validity and as long as 180 days stay duration in China after entry, it is up to the decision of consular officer.

if my reply is wrong, please specify your question clearly.