Soil water content (SWC) is an important factor which affects the growth of crops and also a valuable parameter required for scientific agricultural water management. Therefore, simulation and prediction of SWC are of significance for agriculture. The aim of the paper was to validate the ability of the mechanistic ecosystem model BEPS to simulate SWC of farm lands in areas with a monsoon climate and to investigate the major factors causing uncertainties in simulated SWC. Simulated SWC was compared with measurements in the growing seasons of winter wheat during 2000 to 2004 at Xuzhou agrometeorological station, Jiangsu province. The results showed that BEPS model was in general able to capture the seasonal and interannual variations of SWC, with R2 in the range from 0.1339 to 0.9225, root mean square error and mean absolute error in the range from 0.026113 to 0.06317 and 0.0232 to 0.0525, respectively. Simulated SWC was sensitive to saturated hydraulic conductivity (K) and the parameter b. The reliability and sensitivity of the simulated results depended on the condition of SWC and prepipitation. Simulated SWC was underestimated by the model and its sensitivity to K and b increased during the period with continuously sparse precipitation and low SWC.