A typical subtropical agricultural catchment named Sunjia catchment in Jiangxi province was chosen and the WaSiM-ETH distributed hydrological model was employed to simulate hydrological processes and to quantify interflow at catchment scale. The results suggested that the WaSiM-ETH simulation showed acceptable accuracy and precision in simulation although there were complicated hydrological processes and various land use types in the studied catchment. Relative error of the simulated to measured outflow varied from 3.7% to 4.3%, and linear regression determining coefficient ( R²) reached as higher as 0.96. During the period of 2002-2003, the model predicted annual evapotranspiration ranged from 672 mm to 804 mm, accounting for 39.6%～52.5% of annual precipitation. Annual interflow of the catchment ranged from 542 mm to 666 mm, took 35.4%～39.2% parts of annual precipitation, being higher than 8.8%～21.4% of ratio for annual overland flow. Based on our collective data in this study, we may conclude that the WaSiM-ETH model is flexible and capable of the hydrological simulation in subtropical agricultural catchments as it can not only model the surface hydrological process, but also quantify interflow at catchment scale.