Abstract: Before,the debris flow risk assessment only focuses on a specific time point's risk.Few study analyzed the assessment factors changes and the risk's variations as a result of time change(before or after the debris flow occurring).The paper took Zhouqu Sanyanyu debris flow as a study case,applied the single debris flow risk assessing model;utilized the data of reconnaissance,explorations,and count measures engineering designs;analyzed the risk assessment factors changes at different time points which are before "8.8" disasters,at present,and after count measurements;acquired the parameters of hazards and vulnerability separately;and calculated the risks at these three time points.Finally,discussed the risks assessment results and analyzed the detailed reasons for the risk's variations at different time points.