Numerical simulation on coherent beam combination of multiple fiber amplifiers based on stochastic parallel gradient descent (SPGD) algorithm is carried out. Coherent beam combination of two watt-level fiber amplifiers is experimentally achieved. Phase controlling is performed by SPGD algorithm. The whole system in close-loop performs well. The probability of energy encircled in the target pinhole to be more than 80% of its ideal value is increased from 27.7% to 70.3%, and the energy encircled in the pinhole is enhanced by a factor of 1.57 when the system evolves from open loop to close loop. The feasibility of coherent combination of high-power fiber amplifiers using the method proposed is also discussed.