Water vapor plays a crucial role in atmospheric processes and numerical modeling. On the other hand, it is an inevitable factor to limit the accuracy of high-precision GPS positioning problems. For both issues, knowledge about the amount of atmospheric water vapor is extremely important. In this study, we perform a simulation study to employ GPS signals through a developed tomographic scheme to retrieve 3D structure of atmospheric wet refractivity, which may be assimilated into NWP models for advancing forecasting or position calculation for improving GPS positioning accuracy. To examine the absolute accuracy of our developed tomographic scheme, a well-defined temporal and spatial varying state of atmospheric profile is utilized. Under such an idealized circumstance, ten factors of concern that may influence the retrievals can be easily examined and their impacts may be clearly quantified such as the size of voxels of the studied volume, the cutoff angle of the GPS signals to be used for computation, the values of the positional dilution of precision (PDOP) factors of the GPS signals, the total number of GPS receivers, the influence of additional GPS receivers installed at higher elevations, … etc. Based upon the use of a variety spectrum of adjustable factors, many interesting findings are obtained. For example, the more the number of the observed GPS signals the better the retrievals as expected. Also, the smaller the PDOP value the better the retrievals.