Abstract: The laser four-quadrant detection system is an important part of laser guided weapons. The accurate evaluation of its performance in the design stage is conducive to the iteration and optimization of the design scheme. The simulation model of the four-quadrant detection system was established based on LitghtTools. Through the establishment of target model, optical system model and four-quadrant detector model, the system could be effectively simulated. Combined with principle of four-quadrant detection system, the sum-difference amplitude of angle deviation could be obtained; the stray light of the system could also be simulated to evaluate the impact of stray light on system; in addition, it could also simulate the laser speckle effect and analyze the influence of speckle characteristics on the sum-difference amplitude. Therefore, the modeling and simulation based on LitghtTools provided an accurate basis for design optimization. Finally, the simulation model was verified by experiments. The sum-difference amplitude of the simulation is basically the same as that of the experiment in the range of ± 15°.