To represent the interactions between climate and groundwater, we implemented a groundwater model and a surface runoff model into the regional climate model RegCM3, which is called RegCM3_Hydro.The effects of the groundwater parameterizatious on RegCM3 were then studied based on two 20-year simulations over the east Asian monsoon area conducted using the developed regional climate model RegCM3_Hydro and the original model RegCM3.The comparison of simulated results by the two models shows that incorporating the groundwater model and the surface runoff parameterization into the regional climate model RegCM3 reduces the systematic biases of the simulated mean annual precipitation by 22.2 mm/yr and those of the temperature at 2m by 0.25℃C.Furthermore, RegCM3_Hydro successfully simulated the positive anomaly of the precipitation over Huang-Huai region in 1991 and over the middle and lower reaches of Yangtze river from 1998 to 1999 while RegCM3 did not simulate these anomalies.Obvious seasonal variation is simulated by RegCM3_Hydro in areas with shallow water table depth.