In laser coherent combination,phase detection and control are most critical to master oscillator power amplifier (MOPA). Using heterodyne method,consistence of output beam phase can be ensured through real-time detection and correction of optical phase. The modulator is a liquid crystal optical phase modulator,the wavelength of the main oscillation laser is 532 nm,and the output power of laser can be adjusted continuously from 0 to 6 W. The shifted frequency of the heterodyne system is 40 MHz,and the accuracy for phase control is superior to λ/7. In the process of closed-loop control,a good signal phase correction of optical path has been achieved.