In arid and semi-arid regions, water resources are scarce and unevenly distributed, which limits the sustainable development of regional ecological environment. Vegetation plays a critical role in regulating water redistribution and influencing the water cycle process in the atmosphere-plant-soil system. In this study, Salix psammophila, a typical psammophyte in the Mu Us Sandy Land, was taken as the research object. The water redistribution processes and its influencing mechanism under the influence of canopy and root water uptake were systematically studied through in-situ monitoring, statistical analysis and numerical simulation. Especially the distribution of precipitation by canopy interception and the redistribution of soil water by root water uptake. The results showed that precipitation characteristics and vegetation characteristics were the main influencing factors of canopy penetration rate (Rcp). Rcp gradually increased with the increase of precipitation intensity, and when the amount of a single precipitation exceeded 30 mm or the precipitation intensity exceeded 10 mm/h, Rcp stabilized at about 0.9. When the precipitation amount or precipitation intensity was lower than a certain threshold, the Rcp approached 0, indicating the precipitation was completely intercepted by the canopy and was ineffective precipitation for the soil. When the canopy diameter was greater than 250 cm or LAI was greater than 1.5, Rcp was lower than 0.6, and the influence of canopy characteristics on Rcp showed a decreasing trend with the increase of rainfall intensity. Rcp had an important effect on root water uptake and soil water redistribution. Root water uptake causes a water deficit area in the root zone at a depth of 50 cm, which blocks the deep water infiltration to a certain extent, even less groundwater is replenished. The simulation results of soil water transport at different Rcp levels showed that for the same precipitation event, with the decrease of Rcp, the decrease of soil water storage gradually increased, and the infiltration at 80 cm depth gradually decreased. For the same Rcp level, with the increase of single precipitation, the infiltration at 80 cm depth will increase, indicated that the smaller precipitation and lower Rcp were not conducive to the increase of soil water storage and deep recharge. Only by changed the canopy characteristics, such as reasonable control of vegetation stand density, can the Rcp be increased to increase the effective precipitation reaching the ground. The research results were of great significance for high-quality vegetation restoration and water resources management in arid and semi-arid areas.