The problem about target discretion is very important in many applications. In this paper, detailed research about the effects under some typical atmospheric and ground conditions on the target-background contrast at 0.43-0.75 μm computed by the software package-MODTRAN has been carried out. And the results are provided as following description: the numerical values of contrast present subtle variety according to the seasons shift, and it is easier to identify targets in winter than in summer;both the numerical values and the distribution with wavelength of contrast present alternation according to the atmospheric models;similarly, the aerosol models affect both the numerical values and the distribution with wavelength of contrast.