The beginning of soil destruction is often from the internal destruction of soil particles, and shear strength is an important indicator to reflect soil’s resistance to shear failure. The paper takes shale-derived purple soils in sloping land as the research object and study particle characteristics of purple soil and their mechanism of shear strength by measuring soil particle compositions and shear strengths under different moisture contents and vertical pressures. The result showed that soil particle compositions from summit to footslope were significantly correlated with those of parent rocks. Soil particles <0.25 mm were about 995.65 – 998.62 g/kg, in which particles presented as 0.25 – 2 mm rock fragments were about 439.80 – 510.40 g/kg, however particles presented as 0.25 – 2 mm aggregates were about 6.01 – 80.50 g/kg. With the decrease of elevation, the contents of rock fragments and aggregates in soils did not change obviously. Within soil water content from 7% to 25%, soil water content was negatively correlated with internal friction angle and the influence of soil water content on internal friction angle decreased slowly with the decreased elevation, however cohesion was increased first and then decreased with soil water content increased on single slope, but cohesion did not change obviously with the decreased elevation. Therefore, there are a large amount of <2 mm rock fragments in soil particles in purple soil, and these rock fragments improve soil shear strength while weaken its water sensitivity.