The diffuse reflector system is one important part of the hardware in the loop simulation system of a laser guided weapon.Based on the needs of some simulation system,a grand area indoor diffuse reflector system was developed,which was 6.6 m long and 5.1 m high and was composed of gantry bracket,21 pieces of diffuse reflection board and precise vernier device.With the DT 2 theodolite and other equipments,the verticality of the system was demarcated.The calibration results and some experiments show that the plane is adapted to some kind laser-guided weapon simulation.