In order to solve the problems of insufficient safety durability and limited reinforcement effect of traditional prestressed anchor cable in the application of slope, the methods of indoor and field tests used to investigate the mechanical properties of prestressed steel anchor pipe grouting anchor cable, and the composite reinforcement method of slope was developed. The research results show that the nonlinear variation characteristics of the anchor cable load-displacement curve are more obvious. The change law of loading and unloading stiffness of steel anchor pipe is inconsistent, while the change of loading and unloading stiffness of anchor cable shows the law of power function attenuation. The elastic displacement of steel anchor pipe and anchor cable increases linearly with the load, while the plastic displacement increases with the load in a power function. The field engineering test results of high and steep slope show that the new reinforcement technology is applicable to different slopes. For the complete stratum, the deformation of the anchorage structure is less and the stiffness changes little, the irreversible deformation is small, and the slope deformation is easy to reach a stable state. For broken strata, the fracture increases the slurry permeability, improves the bond strength with the rock and soil, and increases the anchoring force. Therefore, the deformation is large, the stiffness changes greatly, and the irreversible deformation is large. Compared with the traditional anchor cable support, the new support technology can better play the cooperation between different structures. It is concluded that the new reinforcement method can provide reference for slope reinforcement design of similar projects.