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Optical clocks have much better stability and accuracy than microwave clocks.In recent years,great progress has been made in the study of optical clocks.[1-13] However,current optical clocks are passive clocks,[1-12] and their stabilities are limited by the linewidth of the probe laser.[1-15] The thermal noise of the cavity mode hinders the realization of the available narrow-linewidth laser.[13-17] In order to solve this problem,an active optical clock is proposed.[16-21]Active optical clocks,which are novel optical clocks,have attracted more attention recently for their special advantages compared with conventional atomic clocks.[15,17-35] The most interesting point is that the frequency of an active optical clock is insensitive to the thermal noise of the cavity mode.[15,17-21] The quantum-limited-linewidth of active optical clocks can reach the mHz-level,and it is possible to achieve an unprecedent ed-linewidth laser.