In order to clarify the excessive consumption of deep soil moisture by vegetation and the carrying capacity of water resources in arid and water-deficient areas, the Robinia pseudoacacia plantation with a stand density of 1 300 trees/hm² was selected as the research object in the gully area of the Loess Plateau in Western Shanxi Province, and the bare land was taken as the control. The volumetric water content of soil layers in the 0-150 cm range and trunk sap flow of the local R. pseudoacacia plantation were continuously observed by using Enviro-SMART soil moisture location monitoring system and thermal diffusion probe (TDP). Using the ratio of available soil water to water consumption per plant of R. pseudoacacia to measure the carrying capacity of soil water and vegetation of R. pseudoacacia plantation in the study area. The results showed that:(1) Monthly precipitation and monthly soil water storage were the main environmental factors determining soil water and vegetation carrying capacity of R. pseudoacacia plantation, and there was a significant positive relationship between them and soil water and vegetation carrying capacity (P<0.05). (2) According to the soil water and vegetation carrying capacity model of R. pseudoacacia plantation, the soil water and vegetation carrying capacity of 0-150 cm soil layer depth of R. pseudoacacia plantation with 19 years of local age was calculated to be 1 224 plants/hm², slightly less than the actual stand density of the study area (1 300 plants/hm²). In order to ensure that the water consumption depth of the local R. pseudoacacia plantation is controlled within the 0-150 cm soil layer, and to promote the productivity of the local stand at the optimal level, it is suggested that the density of the plantation should be controlled within the carrying capacity of the local soil moisture and vegetation in the future afforestation process, so as to reduce the deep water consumption of the forest land and adjust the balance of soil water resources in the forest land, and promote the rational development of local forestry industry.