Abstract: The mitigation for debris flow not only needs engineering measurements,but also needs monitoring and early warning system,to obtain the goal of risk-reducing effectively.This paper took Zhouqu Sanyanyu debris flow as a studying case,proposed a comprehensive monitoring and early warning system,designed the rainfall monitoring sub-system for the debris flow triggering factors;the infrasound,mud level,ultra red-ray interruption,and video monitoring sub-system for the debris flow occurring and moving;the landslide monitoring sub-system for the debris flow resources;and the dam strain and stress monitoring sub-system for the debris flow engineering count measurements.Finally build up the early warning information system for the whole debris flow.