Abstract: In order to understand the mechanism and process of nitrogen losses from paddy field and upland field, field experiment was conducted in the Zhanghe Irrigation District, Hubei Province of China. The experiment was from June to September 2008, and a dynamic simulation of nitrogen losses in surface runoff from farmlands was carried out using the DRAINMOD model. Results show that both ammonium-nitrogen loss and nitrate-nitrogen loss in surface runoff from the paddy field are higher than those from the upland field. While the loss of ammonium-nitrogen from the paddy field will be higher than that of nitrate-nitrogen, and the opposite is true for the corn field (upland field). The simulated accumulations of nitrogen losses in surface runoff from both farmlands are in good agreement with the observations as revealed by low relative errors and high model efficiency coefficients. Over the paddy filed, the relative errors are respectively 8.35% and 10.99% for nitrate-nitrogen and ammonium-nitrogen; and the corresponding model efficiency coefficients are 0.961 and 0.974, respectively. These values are 5.45% and 14.11% for relative errors and 0.993 and 0.938 for model efficiency coefficients, respectively in the corn field. The study demonstrates that the DRAINMOD model is feasible and effective in the dynamic simulation of nitrogen losses in surface runoff from farmlands in this district.