The gully-slope land is the most active area of soil erosion in small watershed of loess hilly region. It is of great significance to explore the characteristics of soil water cycle under different underlying vegetation types for vegetation restoration on gully-slope land. Based on the hydrogen and oxygen isotope tracer technique, the mechanism of vegetation types affecting soil water cycle in gully-slope land was revealed through field water sample collection and indoor isotope analysis. The results were: (1) The hydrogen and oxygen isotope concentration in the five water bodies decreased in an orderly way, with precipitation being observed to have the greatest amount, followed by soil water of black locust forest, then soil water of grassland, then surface water, finally groundwater. The coefficient of variation of precipitation was the largest, and the coefficient of variation of surface water and groundwater was smaller. (2) Soil water in grassland was mainly recharged by precipitation, accounting for 59.12%. Soil water in black locust forest was mainly recharged by the rising of deep soil water, accounting for 60.97%. Under the condition of short-burst rainstorm, the water transport rate of grassland soil was about 1 cm/d higher than that of black locust forest. And the main transport ranges of soil water in two vegetation types were 0-50 cm. (3) The vertical migration of soil water was the main form of groundwater recharge. The groundwater recharge ratio by soil water of grassland was 51.64%, which was about 0.52% higher than that of black locust forest. It indicated that the vegetation type had certain influence on the characteristic of soil water cycle. Black locust forest had a strong utilization of deep soil water, which might aggravate the dried soil layer of deep soil. And the grassland was more conducive to precipitation infiltration and groundwater recharge. This study can provide a scientific basis for ecological restoration and comprehensive management of gully-slope land in small watershed.