Based on wave radiation transmission theory in random medium and Monte-Carlo method, the optimum extinction characteristics of water fog in multiband is studied. The effect of incident wavelength and particle radium on the mass extinction coefficients of the water fog with lognormal distribution is numerically simulated. And the numerical results is compared with the document data. The transmittance of the laser in the mist is calculated, which is related to wavelength, the width of water fog and the number density. The results show that the multiple scattering must be considered when the number density is thick. The best screening effect can be obtained when the particle radium chosed is closed to the wavelength of the extincted laser. And transmission or reflectivity makes evaluation of the fog more convenient. It has theoretical reference value to the research of the screening performance on smoking.