Shifosi Reservoir is a plain reservoir. High groundwater level in the nearby area caused by impoundment of the reservoir has not only submerged the nearby farmland and village, but also reduced production and affected farmers' living. To analyze the influence of reservoir impoundment on surrounding groundwater level, Visual MODFLOW software was used to simulate the groundwater in Zhujiapu and Chenpingpu areas on the right auxiliary dam of Shifosi Reservoir. Results show that with the rise of the reservoir water level from 45.5 m to 46.2 m and 46.5 m, the area under the critical groundwater table (45 m) in the study area decreased in turn. In 2008, when the reservoir water level was 46.2 m and 46.5 m, the area under the critical groundwater level was reduced by 0.64 km2 and 0.84 km2, respectively, compared with the case of reservoir water level of 45.5 m, and would decrease by 0.38 km2 and 0.45 km2, respectively, by 2022. This indicates that the impact of reservoir impoundment on groundwater level is great. Therefore, relief wells or drainage ditches should be arranged along the auxiliary dam axis to effectively lower the groundwater level, and improve the surrounding ecological environment of the reservoir.