To achieve intelligent monitoring and early warning of mountain slope safety，this article designs a slope monitoring and early warning system based on multi-sensor fusion. The system adopts a“1+N”deployment mode to deploy GNSS reference stations and monitoring stations，integrating multi-source sensing devices such as deep displacement meters and rain gauges，and achieving data fusion through Kalman filtering algorithm. Adopting a hierarchical distributed architecture to establish a four level early warning system，realizing real-time monitoring，data analysis，and early warning information push of slope deformation. Engineering applications have shown that the horizontal displacement monitoring accuracy of the system reaches ±2.3 mm，and the vertical displacement monitoring accuracy reaches ±1.5 mm. The timeliness of warning information push is controlled within 3.5 seconds，which can provide reliable technical support for the safety management of mountain slopes.