Water stress has been the major limiting factor for the sustainable agriculture in the southern part of the North China Plain (NCP). It is a high demand to develop the water-saving agricultural practice for the winter wheat-summer maize double cropping system. Tillage practice has great effects on the soil water movement, water use efficiency, and crop growth, due to the changed soil physical properties and the disturbed soil materials. It is also essential to quantify the soil water dynamics and crop growth processes under different tillage practices for the reasonable tillage system. The objective of this study was to improve the Soil Water Heat Carbon Nitrogen Simulator (WHCNS) model, which was used to simulate the soil water movement and crop growth under different tillage practices. A system evaluation was also made to determine the tillage practices on the water balance, crop growth, and Water Use Efficiency (WUE). The WHCNS model was improved to add the tillage module using Erosion-Productivity Impact Calculator (EPIC) model. Among them, there were the effects of various tillage practices on the change of soil bulk density, soil hydraulic parameter, and soil water content. A two-year field experiment was conducted in the Shangqiu experimental station of Henan province (34°35.222′N,115°34.515′E) on a silty clay soil in the southern part of the NCP from 2015 to 2017. Three tillage treatments were designed, including the Deep Tillage (DT), No Tillage (NT), and Rotation Tillage (RT). Some parameters were measured to calibrate and evaluate the improved WHCNS model, including the soil water storage, Leaf Area Index (LAI), crop dry mass, and yield. The performance of model was then verified by the Relative Root Mean Square Errors (nRMSE), consistency index, Nash coefficient (NSE), and coefficient of determination (R²) between the simulated and measured values. The improved model was then used to analyze the effects of different tillage practices on the soil evaporation, crop transpiration, actual evapotranspiration (ET), crop yield, and WUE of the winter wheat and summer maize. The results showed that there was no significance in the crop yields among different tillage practices. The nRMSE between the simulated and measured values of soil water storage, LAI, and dry mass for all treatments were all less than 30%, the consistency index values were all greater than 0.90, the NSE were all greater than 0.58, R² were all greater than 0.93, and the R2 between the simulated and measured values of crop yields was reached 0.99. Compared with DT and NT in both winter wheat seasons, RT reduced the ET by 8.8%-10.8% and 13.8%-21.0%, and increased WUE by 6.7%-9.4% and 15.7%-24.9%, respectively. Compared with DT and RT in both summer maize seasons, NT reduced the ET by 12.5%-12.9% and 20.7%-22.2%, and increased the WUE by 13.4%-15.2% and 29.1%-31.3%, respectively. In summary, the improved WHCNS model performed the best to simulate the dynamic processes of soil water storage and crop growth under different tillage practices in the NCP. Correspondingly, the WUE of RT was the best performance for the winter wheat, whereas, the WUE of NT was the best for the summer maize. The finding can provide a powerful tool to optimize the field tillage management practices for the water-saving agriculture. [ABSTRACT FROM AUTHOR]