There are a large number of soil and rock mixtures in southeast Tibet, which is a geological slope hazard prone area. The investigation of shear strength index and damage mechanism of soil-rock mixtures (S-RMs) is of great importance for the safe construction of projects and prevention of geologic disasters in highland areas. To investigate the changing law of shear strength of S-RM in Southeast Tibet, soil samples of Yigong landslide body were acquired, six S-RMs with different rock contents(RCs) were made up for straight shear tests, and by analyzing the test data, it was found that the S-RM shear strength was maximum at the threshold RC (75% in this paper). Before the threshold RC, Before the threshold stone content, the higher the stone content, the higher the shear strength of the specimen body, and after reaching the threshold content, the higher the stone content of the specimen, the lower the shear strength of the specimen. Before the critical stone content, the c and φ of the specimen increased in fluctuating type with the increase of stone content, and after reaching the critical content, the c and φ of the specimen decreased with the increase of stone content.