This study aims to explore the influence of plastic mulching on the process of rainfall infiltration in farmland. A rainfall infiltration model was also established using the artificial rainfall soil box test and Hydrus-2D software. Three conditions were set as bare land flat planting, plastic mulching, and ridging plastic mulching. Three factors were selected as plastic mulching width, rainfall, and rainfall duration, each of which was four levels. The levels of each factor were completely cross-simulated to obtain a total of 144 schemes. The rainfall infiltration process of each scheme was simulated to determine the spatial distribution of soil moisture content, the movement of the wetting front, the amount of infiltration after rain, and the change of effective rainfall coefficient. The results show that the Hydrus-2D software presented an excellent fitting effect on each underlying surface treatment of the soil box test. The coefficient of determination, R2 of the simulated and measured values of each treatment was greater than 0.841, while, the Root Mean Square Error (RMSE) was less than 0.015. The improved model was feasible for the rainfall infiltration process under different tillage conditions. Specifically, the moisture content of the surface soil between plastics after rain increased by 5.8% and 9.2% respectively, and the water infiltration depth between plastics increased by 10.67 and 12.45 cm, respectively, compared with the bare land. The water infiltration depth of the underlying surface increased significantly after plastic mulching, with the increase of rainfall. Both plastic and ridge mulching greatly promoted the rainfall infiltration, indicating the more outstanding performance under a large rainfall. There was much more uniform distribution of soil moisture content on the underlying surface of ridging plastic mulching, compared with normal plastic mulching. Therefore, the integrated ridging treatment and plastic mulching greatly contributed to the more uniform water distribution in the soil infiltration after stabilization. The movement rate of the wetting front after rain depended mainly on the change of rainfall and plastic width. The larger the rainfall and plastic width were, the faster the movement rate of the wetting front was. Both ridge plastic mulching and furrow increased the moving distance of the wetting front, but the contribution rate of infiltration decreased with the increase of rainfall. There was a relatively small contribution rate of ridge and furrow to the infiltration when the rainfall was 30 mm. Both ridgeless and ridgeless mulching relatively promoted the rainfall infiltration. Nevertheless, there was an outstanding effect of ridgeless mulching on the rainfall infiltration. Among them, the maximum infiltration was observed, when the plastic width was 70 or 80 cm. The plastic mulching and ridging plastic mulching significantly improved the effective rainfall coefficient in the light rainfall compared with the bare land flat planting. A significant level was achieved in the effect of different plastic widths on the effective rainfall coefficient, the maximum of which occurred at the plastic width of 70 cm. Therefore, the width of mulching plastics, ridges setting, and ditches can be expected to greatly increase the amount of rainfall infiltration and the depth of water infiltration, particularly for the higher use efficiency of the rainfall resources and farmland water. The finding can provide a strong reference for the farmland water movement and rainfall infiltration on different underlying surfaces, in order to alleviate the agricultural water shortage in arid and semi-arid areas.