Ms.SHEILAHSP, you can extend your multiple entry visa for another 2 weeks at the local Exit & Enter Department under Public Security Bureau, in fact, you are issued a single-entry visa with 2 weeks stay duration, then the previous 6 months multiple entry visa will automatically expires, you can't use the visa to enter China again during its validity. The best way is exit mainland China to Hk or Macau when the 30 days stay duration is up, then enter Mainland China again for another 30 days for the re-entry.