Abstract: Constructing a rational conceptual model of hydrogeology is very important for the numerical simulation of groundwater. If the conceptual model is not reasonable, the whole numerical simulation will be meaningless. Generally, the conceptual model of hydrogeology can be roughly determined by hydrogeological investigation. However, it cannot be determined by the hydrogeological investigation for some recharge sources which are not easy to be found. The water chemistry and isotope characteristics are good indicators for the groundwater recharge and the flow path. Based on these characteristics, the hydrogeological conceptual model can be refined. In this paper, groundwater sampling and isotopic characteristics of groundwater in the study area were analyzed. Then the concealed groundwater source was identified, and the permeability of the top silty clay layer was determined. On the basis of the above results, the boundary conditions of the conceptual model of hydrogeology were refined. This is of great significance to get the correct simulation results of groundwater flow and solute transport in the later stage.