In order to provide some theoretical basis for controlling water and soil erosion on the Loess Plateau, the process of soil moisture responding to precipitation in the loess region of western Shanxi Province was studied through a series of field slope rainfall experiments. In the experiments, the soil moisture in the loess region of western Shanxi Province was continuously positioning observed. The results showed that: 1) slope soil moisture content was obviously affected by the density of vegetation. Compared with the forest with low vegetation density or bare land, the response of slope soil moisture to precipitation in the forest with high density was comparatively gentle. 2) In vertical direction, the response of soil moisture content to precipitation was most direct and rapid in the layer ranging from 0 to 20 cm. With varied vegetation density, the soil moisture content of subsurface (10-20 cm) of each measuring point increased sequentially. Compared with the surface layer(0-10 cm), the curves of soil moisture content rising in subsurface were delayed and extended, reflecting the successive process of soil moisture infiltration. The response of soil moisture content to precipitation in the deeper layer (20-150 cm) was almost nonexistent. 3) The response of soil moisture content to precipitation in surface layer on the slope was affected by rainfall intensity and vegetation density. When the rainfall intensity was low, the variation process of soil moisture content can be divided into two periods: rising and decreasing; while when rainfall intensity was high, the process exhibits three periods: rising, steady and decreasing. The arrival time of each period lagged with the vegetation density increasing.