Abstract: This study proposes to explore the effect of interface angles β on the triaxial mechanical properties of backfill and surrounding rock combined bodies(backfill-rock combined bodies)by conducting a triaxial compression experiment of backfill-rock combined bodies with interface angles β of 0°, 15°, 30°, 45° and 60°. This paper compared and analyzed the mechanical properties, failure characteristics and strength evolution patterns of the combined bodies with different interface angles. The experimental results show that: When β≤30°, the stress-strain curve of the combined bodies can be divided into four stages: pore compaction, elastic deformation, plastic deformation and failure development. Its failure characteristics are mainly compression shear failure of the backfill. With the increase of the interface angles, the combined bodies stress drops steeply after reaching the peak strength, without significant plastic deformation or failure development stage. Its failure characteristics gradually change from compression shear failure inside the backfill to sliding failure along the interface. The peak strength of the combined bodies first increases and then decreases with the increase of the interface angles, and peak strength reaches a maximum value when β=30°. Based on the theory of single weak plane, the interface critical angles for sliding failure of the combined bodies is 57° to 68°. Where β=60°, the combined bodies occurred sliding failure surface along the interface, and the results from theoretical calculation confirm the experimental results.