Phase-locking and coherent output of two fiber lasers are studied. Two fiber laser are coupled into a common self-imaging resonator with a spatial filter for mode selection. The resonator consists of two collimators with 8 mm focal length, a Fourier lens with 500 mm focal length, and a coupled output mirror. The filter is made of two platinum wires with 20 μm diameter and is placed at the plane of the output mirror. The high-contrast interference strips of the beam profile are observed. Under the output mirror with the different reflectivity of 50% and 30% condition, the slope efficiencies of the individual laser and the laser array are analyzed. When the whole pump power is 60 W, a high coherent power output of 18.3 W is obtained. Steady phase-locking results from a self adjusting process of the laser array which adapts to changes in the optical path lengths. This experiment shows that the coherent power output can be improved greatly by means of this method.