The fracture behavior of the mass rock-concrete interface is essential for assessing the safety of concrete dams built on bedrock within the framework of fracture mechanics. The presented study investigates the fracture characteristics of the mass concrete of the size φ450 mm*450 mm and mass concrete-basalt interface of the size φ470 mm*450 mm cylindrical composite specimens containing preset cracks through direct tensile tests on a 15MN MTS servo-controlled testing machine. The system displacement was used as the control parameter for the tests. The load-crack mouth opening displacement (P-CMOD) curves and load-loading point displacement (P-δ) curves were obtained by four elongation displacement gauges and four laser displacement gauges, respectively, from which peak loads were determined and energy absorption capacity and fracture energy were calculated, and then the fracture toughness compensating for the effect of eccentricity in the tests was obtained by combining numerical simulation. The results indicate that for mass concrete-basalt specimen, the concrete slurry embedded in basalt is pulled out during the test, with the basalt surface exhibiting cement slurry adhesion and roughness. The fracture toughness taking into account the influence of eccentricity is significantly increased compared to not during the test. The fracture toughness, energy absorption capacity and fracture energy of composite specimens were significantly reduced compared to mass concrete.