The phase-locking of two photonic crystal fiber (PCF) lasers is studied experimentally by using Michelson cavity technique, and 47 W coherent output power is obtained. The phenomenon of interference-enhancement and interference-loss on the two arms of the Michelson cavity is theoretically explained by analyzing the optical path difference. Experiment shows that the Michelson cavity setup can improve the spectra of the combined laser significantly. The bandwidth of the combined laser is less than 5nm in our experiment.