In view of the fact that the stress of the pile-soil interface changes due to unloading or upper stacking load of soil around the pile, which leads to the damage of the peak shear strength of the pile-soil interface and decreases to the residual strength, a shear test has been carried out by the self-made shear device of the research group so as to study the effects of normal stress, compactness, moisture content and preloading on the residual strength of pile-soil interface. The results show that a softening effect can be observed with the shear stress reaching the peak strength. The greater the normal pressure is, the more pronounced this softening effect will be. The residual strength will be improved with the increase of normal stress and degree of compaction of soil, showing an initial increasing and a subsequent decreasing trend with the increase of water content, until finally reaching the maximum near the optimal water content. Under different normal pressures, due to the influence of moisture content and degree of compaction, the residual strength is characterized with a peak distribution, reaching the maximum near the optimal moisture content and the maximum at the maximum degree of compaction. When the normal pressure of preloading is relatively small, the proportion of residual strength will be higher. Based on a study on the normal stress residual strength and normal stress residual stress ratio under different degrees of compaction, it is concluded that there is a significant linear relationship between the residual strength, the residual strength after considering preloading and the normal stress. The shear failure of the interface conforms to the Mohr Coulomb shear failure criterion. Under is different degrees of compaction, the residual stress ratio decreases with the increase of normal stress, meanwhile the decrease more is obvious under the influence of preloading.