Now GIS is turning into a good tool in handling geographical, economical, and population data, so we can obtain more and more information from these data. On the other hand, in some cases, for a calamity, such as hurricane, earthquake, flood, drought etc., or a decision-making, such as setting up a broadcasting transmitter, building a chemical plant etc., we have to evaluate the total population in the region influenced by a calamity or a project. In this paper, a method is put forward to evaluate the population in such special region. Through exploring the correlation of geographical parameters and the distribution of people in the same region by means of quantitative analysis and qualitative analysis, unit population database(1km×1km)is established. In this way, estimating the number of people in a special region is capable by adding up the population in every grid involved in this region boundary. The geographical parameters are obtained from topographic database and DEM database on the scale of 1:250 000. The fundamental geographical parameter database covering county administrative boundaries and 1km×1km grid is set up and the population database at county level is set up as well. Both geographical parameter database and unit population database are able to oiler sufficient conditions for quantitative analysis. They will have important role in the research fields of data mining(DM), Decision-making Support Systems(DSS), and regional sustainable development.