Abstract: The cloud-and-fog scattering effect will produce laser signals resulting in false alarm for laser fuse. Based on the Monte-Carlo technology, backscattering signals of clouds and fogs are simulated and compared with results of the experiment carried out in the cloud-and-fog chamber. Results show that the pulse broadening effect mainly introduced by multiple scattering is drastical when the transmitting pulse width is less than 10 ns. And the theoretically calculated data are in good agreement with the experimental data. The temporal shapes are both close to Gaussian shape, and theoretically calculated results differ from experimental results by less than 6% for the width of the backscattering signal and 30% for the intensity of the backscattering signal.