Abstract: Abstract: Pisha-sandstone is a kind of loose rock stratum. Since the rock stratum is thin and low in pressure, it is hard to form rock, poor to glue the sandstone and low in structural strength. In nature, the stratum is apt to become muddy when encountering water and to form sands when encountering wind, consequently resulting in severe erosion. Geological disasters happen continually due to unsteady margins of Pisha-sandstone area, and its peak strength and residual strength are the important indexes in the assessment of the stability of landslides. The strength is in close relation with its density, particle diameter, contact pressure between particles and moisture contents. According to China's general scheme of soil fraction, the Pisha-sandstone is graded into coarse sand (≥0.5?1 mm in diameter), medium sand (≥0.25?0.5 mm in diameter), and fine sand (<0.25 mm in diameter). Under four moisture contents (5%, 8%, 11%, 14%), recurrent direct shear tests were performed on Pisha-sandstone by using the Digital Direct/Residual Shear Apparatus to investigate its changing laws of peak strength and residual strength. Based on the particle diameter of Pisha-sandstone soil, the recurrent direct shear tests were performed on three ranges of particle diameters (≥0.5?1 mm, ≥0.25?0.5 mm, <0.25 mm) under the pressure at 50, 100, 200 and 300 kPa. We found that among the four recurrent direct shear tests of Pisha-sandstone at the same particle diameter, the peak value of shearing stress appeared at the first shear in different ranges of particle diameter; the peak value of the fourth shear was very similar to that of the third shear, and the shear strength of the fourth shear was actually the residual strength. When the particle diameter was between ≥0.5?1 mm and moisture content at 5%, the peak value appeared at the first shear, which tended to be strain softening. With the increase of normal pressure, the strain softening increased. At the same moisture content and normal pressure, the shear strength and residual strength of the Pisha-sandstone differed from its particle diameters, which were lowest in the diameters ≥0.25?0.5 mm. For the Pisha-sandstone of same particle diameter, the peak strength and residual strength were increased with the decrease of moisture content. In the particles at the diameter ≥0.5?1 mm, the peak strength varied with the moisture content. In the particles at the diameters ≥0.25?0.5 mm and <0.25 mm, the shear peak slightly reduced with the moisture content. When the moisture content was lower than 11%, the residual strength of Pisha-sandstone did not change significantly. When the moisture content was over 14%, the residual strength of Pisha-sandstone in three diameters were significantly reduced, especially in the Pisha-sandstone in the diameters ≥0.5?1 mm. Therefore, 11%?14% were the critical values of moisture content, during which the residual strength of Pisha-sandstone was apt to change dramatically. Moreover, the functional relationship between normal displacement and shearing displacement was achieved and analyzed by SAS software, which can better reflect the dilatancy law of Pisha-sandstone in the shearing process.