The stochastic parallel gradient descent (SPGD) algorithm is introduced,and the 2-channels master oscillator power amplifier coherent beam combination (MOPA-CBC) system based on this algorithm is designed. This system adopts a 10 W stage ytterbium fiber amplifier to import the phase noise. And the LiNbO3 phase modulator is adopted to compensate the piston error. When loop is open,the phase noise is analyzed at different working stages of amplifier. After loop closed,the stable coherent combined beam is obtained,the intensity of which increases 1.5 times than before,and piston peak-to-valley (PV) value decreases to 100.8 nm. The precision of correction reaches 1/(10λ),and the bandwith is 100 Hz. The experimental results indicate that the control ability of SPGD algorithm is effective in phase-locking.