Optical system of high power laser was designed and optimized.Through theoretical analysis and field experiment,the focusing characteristics of ellipsoidal mirror optical system was studied and compared with the traditional optical system based on parabolic mirror.The transmitting system was optimized.The focusing spot of optical system was theoretically calculated and simulated,and the laser spot size and power density are analyzed in two different systems.Finally,the design results were verified by field damage experiments.The experimental results show that the high power laser optical system based on ellipsoidal mirror has smaller diffraction spot resolution and higher energy concentration.