Michelson cavity technique provides an effective solution for coherent beam combination. In this paper, coherent beam combination of two fiber lasers by using an all-fiber Michelson cavity technique is demonstrated, and 11.75 W coherent output power with a coherent combination efficiency of 95.76% is obtained. The influences of the relation of coherent combination efficiency to laser cavity length difference, and the pump symmetry on coherent combination efficiency are studied experimentally. Experimental results show that the coherent combination efficiency is highly sensitive to the influence of laser cavity length difference, that the difference in combinination efficiency, induced by laser cavity length difference, can be as large as 18%, and that there is an optimal cavity length difference. The maximal influence of pump symmetry on coherent combination efficiency is within 2%, which can be neglected.