Dynamical simulation on coherent beam combining of multiple fiber amplifiers based on stochastic parallel gradient descent (SPGD) algorithm is carried out. The influence of phase noise with different amplitude and frequency on the control bandwidth is computed,and the relationship between control bandwidth and laser numbers and iteration rates of the algorithm is analyzed. The results show that the control bandwidth decrease as an increase in the amplitude or frequency of the phase noise,the value is in proportional to N-4/3 and iteration rate,where N is the laser numbers. The computing results present a reference for scaling coherent beam combining based on SPGD algorithm to high-power,large-number of laser beams.