Chinese visa re-entry after 60 days.

Sorry if answered already. My Visa is valid 10 years. I have 60 day one. I used the 60 day one with 9 years and some months left valid.
May I enter China again under same valid entry permit even though I used the 60 days already?
My Visa says M for multiple entries.
If so when can I go back for another 60 days? My friend and I are not sure.