The single-scattering theory is always used to study the non-line-of-sight(NLOS) light propagation,but when it is used for long distance or under complicated weather,much larger error will occur.In the paper,the NLOS light propagation model based on Monte Carlo method is described in detail.This model is not only accordance with single-scattering model under short distance and clear weather,but also in good agreement with the comparative experimental results,which also illustrates the correctness and efficiency of this algorithm.