Abstract: In order to explore the direct shear performance and failure mechanism of the interface between magnesium phosphate cement (MPC) concrete and normal concrete (NC), seven MPC concrete-NC specimens are designed for the direct shear test. Combined with digital image correlation (DIC) measurement technology, analyzing the effects of interface treatment methods and steel fiber on interface failure mode, on direct shear bearing capacity and shear-slip, and comparing the test results with the calculated values of existing specifications. The results show that under the action of shear loading, the failure modes of the specimens are interface shear failure, the unreinforced specimens are brittle failure, and the reinforced specimens are plastic failure. Compared with the chiseling interface, the direct shear strength of the groove, of keyway and of planting bar specimens is significantly improved, and the shear slip performance is perfected. The direct shear strength of the groove specimen is the highest. The incorporation of steel fiber enhances the interfacial adhesion of concrete, delays the crack propagation, and significantly improves the interfacial shear strength. Based on the test data, the calculation formula for the direct shear bearing capacity of MPC concrete-NC interface is proposed on the basis of existing specifications. The calculated values are in a good agreement with the experimental ones, which verifies the validity and accuracy of the calculation formula proposed.