A scheme of all-optical clock recovery based on an all optical fiber mode-locking cavity configuration is analyzed and demonstrated. In the scheme, the semiconductor optical amplifier (SOA) in traditional structures is displaced by a segment of highly nonlinear optical fiber (HNLF). Through the cross-phase modulation effect (XPM) in optical fiber, the nonlinear modulation is implemented in the cavity, which is able to overcome the limitation of date rate caused by the carrier recovery time of SOA in traditional methods and break through the "electronics bottleneck". The theory of cross phase modulation effect in optical fiber and the principle of clock recovery in mode-locking ring cavity are analyzed. In addition, a high quality clock signal is successfully extracted from a 40 Gbit/s optical return-to-zero (RZ) signal experimentally. This scheme can work straightway with higher bit rate.