Abstract: The shear characteristics of the cemented tailing backfill (CTB)-rock interface play a crucial role in the design and stability of underground goaf. To investigate the shear behavior of the CTB-rock interface, three-dimensional morphology scanning and engraving techniques were used to construct rock samples representing the topography of surrounding rocks. Through a series of direct shear tests on CTB-rock samples to examine the influence of the cement-tailings ratio on the interfacial shear behavior. The results indicate that the compressive strength of the CTB and the shear strength of the CTB-rock interface decrease as the cement proportion decreases. With the decrease of cement content, the failure area of the CTB after the test increases and the roughness of the newly generated interface decreases. Digital Image Correlation (DIC) analysis revealed that compression stress concentration in the region with the obtuse angle with shear direction is the primary cause of CTB failure. Moreover, the correlation between the wear area and the dense silicon particle area confirms that silicon particles are more prone to failure than other regions. This research provides new insights into the shear sliding mechanism at the CTB-rock interface and the selection of the cement-tailings ratio in engineering sites. For example, if the horizontal principal stress of the surrounding rock mass is a relatively high value for the backfilling area, the cement content can be reduced for the application of the CTB.