Abstract:In this paper, four sampling plots with different slope directions and different densities were selected as the research object in the Caijiachuan watershed of the loess area in western Shanxi Province. An observation point was placed at the center of each plot, and the soil volumetric water content from January 2016 to December 2016 were determined by the TRIME-TDR soil moisture analyzer. The soil moisture in each 0—200 cm soil layer was determined stratified with every 20 cm respectively in the early, middle and late of each month. Four sampling plots were studied about the seasonal variation of soil moisture, the vertical variation in soil profiles, and the effects of slope directions and densities on soil moisture. The results showed that: (1) Seasonal changes of soil moisture could be divided into four periods including stationary period, consumption period, fluctuation period and recovery period, the annual maximum soil moisture was in the same month of the maximum rainfall in the year, and the seasonal distribution of precipitation had effect on soil moisture. (2) Soil layers could be divided vertically into three layers, including severe-changing layer, weak-changing layer and relatively stable layer. With the increasing soil depth, soil moisture increased first, decreased next, and then leveled off. (3) The slope directions and densities had significant effects on soil moisture. Soil moisture on shady slopes was significantly higher than that on sunny slopes (P<0.01). Low-density soil moisture was significantly higher than the high-density (P<0.01).