Xiangjiaba hydropower station is one of the cascade power stations on the Jinsha River, China. Due to the complicated geological conditions of its dam foundation, evaluating the rock mass quality and determining the mechanical parameters of rock masses are very important issues. To address these issues, several groups of rock borehole shear tests (RBSTs) were conducted on the black mudstone in the dam foundation of Xiangjiaba hydropower station in the second construction phase. Forty three groups of shear strengths of black mudstone samples were obtained from RBSTs, and the shear strength parameters (c and f ) were calculated using the least squares method. In addition, the limitations and merits of RBST employed in the Xiangjiaba hydropower station were discussed. Test results indicate that the shear strength parameters obtained from RBST have a good correlation with the results from sound wave test in borehole. It is believed that RBST has a good adaptability and applicability in geotechnical engineering. Xiangjiaba hydropower station is one of the cascade power stations on the Jinsha River, China. Due to the complicated geological conditions of its dam foundation, evaluating the rock mass quality and determine the mechanical parameters of rock masses are very important issues. To address these issues , several groups of rock borehole shear tests (RBSTs) were conducted on the black mudstone in the dam foundation of Xiangjiaba hydropower station in the second construction phase. Forty three groups of shear strengths of black mudstone samples were obtained from RBSTs, and the shear strength Parameters (c and f) were calculated using the least squares method. In addition, the limitations and merits of RBST employed in the Xiangjiaba hydropower station were discussed. from sound wave test in borehole. It is believed that RBST has a good adaptability and applicability in geo technical engineering.