Scattering effects of clouds and fogs produce the backscattering signal which results in false alarm for laser fuse. Based on the Monte-Carlo technology, cloud-and-fog scattering effects are simulated, and rules of wave shape and peak power of cloud-and-fog scattering echo variable with baseline distance are qualitively given. Results show that peak power and pulse broadening extent of the laser echo goes up with pulse width increasing. However, when pulse width increases to 50 ns, peak power is saturated. Simulated results may provide target discrimination and optimized design of detecting threshold and transmitting pulse width for laser fuse with reference.