Abstract: Based on the soil-plant-atmosphere continuum and soil water dynamics theory, considering crop root extension and root water uptake, a dynamic two-zone model was built, which divided the soil moisture changing layer into two zones, namely, the active root zone and moisture storage zone. In the active root zone, the variation of the dynamic soil moisture with the depth change of crop root zone was described. In the moisture storage zone, the water flux on lower boundary of the root zone which indirectly has effects on crop evapo-transpiration was analyzed. Using the soil moisture of the storage zone as the model variable, the simulation fitting error as objective function, the optimization model parameters were solved using Free Search method. A comparison between the simulation results of the dynamic two-zone model and the observed values showed that the proportion of relative errors less than ± 5% is of 49.09% and ± 10% of 94.55% respectively. The t test indicated that the predicted values and the observed values had good consistency. The regression analysis indicated that their correlation coefficient was 0.779. These results show that the model has a high simulative precision.