Based on Fourier transform optics, a method to improve coherent combination efficiency in paralleltransmission system is introduced. According to the knowledge of laser optics, the influence of the method on lasercoherent combination efficiency is calculated by numerical value simulation. Numerical simulation of the paralleltransmission system and the lens system shows that the method described in the passage indeed improve the effi.ciency, with limitation that equals the efficiency in lens system. Different initial phase schemes lead to different ef.fect, and the best scheme is got by comparing.