Abstract: The agricultural drainage in Ningxia irrigation district is a main contributor of non-point source pollution to the Yellow River and other surrounding water bodies. In order to improve water management situation, rice fields drainage process simulation in Yinnan irrigation districe was analyzed with DRAINMOD model recommended by USDA. Results show that the simulated drainage volume from the field ditch is extremely close to the observed value, and the relative error of annual drainage volume is only 0.4%; the Nash Sutcliffe's coefficient for daily water table is 0.86. The drainage volume from previous analytical approach was also analyzed, but the relative error was as high as 36%. The reason is that the daily water table fluctuation could not be considered with the analytical method, and using a single average water table resulted in over-estimation of the drainage. This study demonstrats that the model can describe the drainage process more precisely and evaluate the long-term behavior more flexibly.