Abstract: The number concentration of dust aerosol particles is hard to be directly measured, but it is one of the most important factors affecting the laser transmission characteristics. Based on the mass concentration of dust aerosol particles, using the size distribution of particles, the formula for calculating the number concentration of particles was deduced. Under the condition of sand and dust, the transmission characteristics of laser was studied by using Mie theory and Monte Carlo method, the relationship of the transmission attenuation and transmittance with wavelength and the mass concentration were analyzed, curve of visibility along with particle mass concentration was given, and the calculation results of Mie theory and Monte Carlo method were compared. The results show that, in the choice of several wavelengths, the transmission attenuation is minimum when wavelength is 10.6 m (about 58% of that in the 1.06 m), with the increase of mass concentration, the visibility decreased rapidly and then decreased slowly, whose trend is near hyperbolic curve. The method, basing on the mass concentration of particles(this parameter can be measured directly), can calculate the laser transmission characteristics of dust aerosol, which has very important theoretical significance in practical application.