Research on scattering characteristics of sand and dust in the infrared waveband has important theoretical significance for Free Space Optical(FSO) communication. According to some infrared wavelength commonly used in FSO, its scattering characteristics in different particle sizes of sand and dust were analyzed by Mie theory; based on log-normal distribution model of particle size, the attenuation coefficient of laser in waveband 0.76-10.6 μm were calculated under the condition of sand and dust. The results show that: the transmission attenuation near waveband 7.4-8.0 μm are minimum under the condition of sand and dust, and it′s significantly lower than that in other wavebands. Therefore, the laser in waveband 7.4-8.0 μm should be chosen to be used in FSO under the condition of sand and dust, for that its transmission performance will be obviously better than that in other wavebands. At last, take wavelength 1.064 μm as an example, the "visibility" with the change of particle concentration was analyzed, and the result was compared with that by Monte Carlo method.