Abstract: From the point of view of Fourier optics,laser beam coherent combination by binary phase grating is discussed and the design method of phase grating is studied.Using the genetic-simulated annealing algorithm,the optimum parameters of grating are obtained.Then,the simulation results of diffraction and combination are presented.The error analysis shows that it will influences the diffraction efficiency.For laser beam combination,binary phase grating is simple,flexible and can greatly improve the laser beam's power density and the system integration.