The model of laser relay mirror system is established, to calculate the effect of telescope solid-state laser relay mirror system and the conventional high energy laser system on 1-km altitude,1-km/s speed target by using the “4-D” code of the laser atmosphere propagation. Because the relay mirror system has long time effect on the target, its damage threshold standard for 3-cm bucket power is 28.27 kW and 5.655 kW. The analysis results show that the coverage range of the conventional high energy laser system is 4.6 km, and the coverage range of laser relay mirror system is 11.3 km. Compared with the conventional high energy laser system the relay mirror system reduces the influence of the atmosphere on the laser, and opens up the coverage range of the laser system.