The survey, construction, operation and maintenance of railway construction in complex and dangerous mountainous areas are difficult, and geological hazards along the line occur frequently. The geological hazards at slopes of the tunnel entrance and exit are particularly prominent, which are characterized by dispersion, frequent occurrence and great harm, and have become the key risk factors restricting the construction and operation of railway tunnels. Based on the concept of risk prevention and control of gateway forward and whole life cycle, InSAR technology, lowaltitude UAV technology, and analytic hierarchy process are applied to assist the monitoring of slopes, identification of geological hazards and risk assessment of dangerous rocks in the stages of site selection, tunnel access construction and operation. It is helpful to systematically and efficiently grasp the development and distribution characteristics of geological hazards in the tunnel site area, especially for the precise prevention and control of various geological risks on slopes of the tunnel site area. After the practical application in the ChengduKunming railway double track and other railway tunnel projects, the ultraremote automatic monitoring accuracy has reached millimeter level, the identification accuracy of potential or existing geological disasters has been greatly improved, and the identification accuracy of dangerous rock risk sources on the tunnel slope can effectively guide the geological risk prevention and control at the tunnel portal.