Based on the high-density observation method of soil moisture on natural slopes, this study clarifies the dynamic characteristics, spatial and temporal stability, and influencing factors of soil moisture on the natural slopes of Platycladus orientalis in Beijing mountainous areas. It is necessary to provide a basis for the assessment of the impact of ecological restoration on hydrology and water resources in the earth-rock mountainous area of northern China. Taking the slope (40 m×50 m) of Platycladus orientalis forest land in Beijing Jiufeng National Forest Park as the research object, 30 measuring points in the natural slope were measured by Diviner 2000 and the soil water content (SWC) above gravel layer was observed from August 2014 to March 2016. The results show that the soil water storage (SWS) has visibly seasonal variation characteristics and is consistent with the quantitative value change trend; the average SWC of different soil layers is in intermediate variability and the SWC variability decreases with increase in SWC. Soil moisture has a high time stability during the entire observation period. The No.2 measuring point located on the horizontal slope is the most representative of the average soil moisture in the study area. With the increase of the distance from the tree, the SWS gradually increase. In spring, summer, and autumn, the SWS at the distance of 0.5 m and 1.5 m from the tree is significantly different (P<0.05). SWS of the horizontal level is significantly greater than SWS of the steep slope (P<0.05), and the SWS on the downslope in summer and autumn is significantly lower than that of the upslope (P<0.05). Soil and water conservation engineering measures have important influence on the SWC distribution pattern on the slope.