Although aerosols have great impacts on Surface Downward Shortwave Flux (SDSF), the relationship between aerosol loading and SDSF in global models has not yet been adequately investigated. In the present study, we attempt to investigate/estimate the effects of aerosol optical thickness (AOT), single scattering albedo (SSA) and amount of precipitable water vapor (PWV) on SDSF through an integrative comparison and analysis of a global aerosol-transport model, SPRINTARS, a radiative transfer model, Rstar, and in-situ measurements, AERONET and BSRN. We found that the AOT difference usually has the strongest impact on the SDSF difference and the SSA difference has a moderate impact over heavy aerosol loading regions, whereas the effect of water vapor can be ignored. Finally, we generated a contour plot to demonstrate the relationships between AOT-SSA-SDSF. For example, at low AOT (e.g., 0.15), the 20 Wm-2 changes in SDSF are required to make more than 0.2 changes of SSA, whereas at high AOT (e.g., 0.85), the same changes in SDSF are required to have only 0.05 changes of SSA.