Abstract: The soil is easy to peel off when the external-soil spray seeding (ESSS) technology is used to restore the high and steep bare rock slope. The application of microbial mineralization technology to form microbial mortar on bare rock surface has the potential to improve the adhesion and stability of sprayed soil substrate and rock surface. The experiment of cementing rock surface with microbial mortar was carried out to investigate the change of shear strength and cementation mechanism of the interface between microbial mortar and rock. The results show that the calcium carbonate content in the microbial mortar is about 3.3% after coating the limestone with microbial mortar and spraying the cementing solution with a concentration of 1.0mol/L three times. Meanwhile, the cohesion and friction angle of the microbial mortar-rock interface are 45.6kPa and 26.40˚, respectively. The cohesion of the microbial mortar-rock interface is linear positively correlated with the calcium carbonate content. Microbial cementation has little effect on the friction angle of the interface. The disintegration ratio of microbial mortar is negatively exponential correlated with the calcium carbonate yield. When the calcium carbonate content is higher than 2.5%, the microbial mortar has better water stability. The calcium carbonate crystals in the microbial mortar form a bridge bond between the sand particles and the rock surface, which is the main source of the shear strength of the microbial mortar-rock interface. There are abundant pore in the microbial mortar overlying the rock surface. The interfacial shear failure is mainly caused by the peeling of the contact surface between the sand particles and the calcium carbonate crystals, and the internal fracture of the calcium carbonate crystal aggregate. The research results can provide reference for the application of microbial geotechnical technology in the ecological protection of rock slopes.