The invention relates to a monitoring and prewarning system and a monitoring and prewarning method for geological disasters. The monitoring and prewarning system for the geological disasters comprises a plurality of global navigation satellite system (GNSS) monitoring stations 1, a continuous operational reference system (CORS) 2, a 3rd-generation (3G) wireless network or wireless bridge 3, a microwave communication system 4, a monitoring and prewarning server 5, a monitoring and prewarning central computer 6 and the like which are arranged in a monitored area. Each GNSS monitoring station 1 comprises a global positioning system (GPS) receiver 11, a 3G network transmission component 12, video monitoring equipment 13, a microwave communication transmission component 14, a power supply 15 and the like. In the method, the aims of forecasting and prewarning possibly initiated geological disasters automatically in real time can be fulfilled by setting the GNSS monitoring stations in areas liable to the geological disasters, monitoring ground surface displacement in real time by the CORS, performing real-time ground surface displacement monitoring on the geological disasters, such as collapse, landslide, debris flow, surface collapse, subsidence, ground fissure and the like, which can be caused by ground surface displacement, combining remote video monitoring, performing data processing on monitoring information, and automatically issuing prewarning information.