A scheme of all-fiber laser coherent combining system based on fiber-loop is put forward and passive coherent combining of four fiber laser beams is realized in all-fiber configuration with home-made fiber amplifiers. The power, spectrum and far-field beam pattern of the combined open loop and closed loop as well as the bandwidth of passive phasing are also investigated. When the system is in open loop, the output power varies from 71 mW to 271 mW. When the system is in closed loop, the output power is around 412 mW. The output power with system in closed-loop state is quite stable, and 2.1 times higher than the average output power in open-loop state, indicating that the scheme can realize stable phase locking. The bandwidth of the system is over 50 kHz, implying good ability of passive phasing. By improving the power of the amplifiers and adopting combiners with higher handling power, it is possible to obtain coherent combining output with higher power.