激光引信在降雨中工作时会受到雨滴的散射和衰减效应，使光束质量变差，回波能量减小，从而影响探测系统的性能。以蒙特卡罗方法为基础，给出了激光在降雨中的传输模型，分析不同模拟条件下光束的扩展特性，并进行实验测试。由仿真分析可知，雨滴对光束的散射作用导致光斑扩散，从而光束能量密度减小，并且随着降雨强度、传输距离和光束发散角的增大，光子散射次数增多，光斑直径扩大，到达接收面的光子减少，光束能量衰减。实验测试结果与仿真计算基本一致，最大误差不超过4%，很好地验证了模型的准确性。

The laser fuze working in the rain would be scattered and attenuated by the raindrops, so that the beam quality will decrease and echo power reduce, consequently affect the function of detecting system. Based on Monte-Carlo method, the transmission model of laser in the rain is founded, and beam spread characteristics at different simulation conditions are analyzed, and the model is validated by experiments. The simulation results indicate that the raindrop scattering induced to beam spread and power density decreasing, and along with the augment of rainfall rate, transmission distance and beam divergence, the photon scattering times increase and spot diameter extendes, the photons arriving at the receiving surface decreases and beam power attenuates. Experimental results are consistent with the simulation calculations and the largest error is not more than 4%, which greatly agree with the model.