The geological model of the dynamic reserve of debris flow material source including downward induced block collapse and lateral erosion induced slide and sloughing was established on the basis of the classification of the debris flow material source which come from landslide,rock falls and deposits on the slopes.44 debris flows in Wenchuan earthquake region were selected to analyze the correlation of the dynamic reserve and the total amount of the debris flow material source,which was proposed as the linear relationship.according to the statistics of the analysis,the dynamic reserves is up to 15%,30%,37% and 40% when the total amount of material source is less than 50*104m3,100*104m3,200*104m3 and 300*104 m3.The graphic calculate method for confirming the dynamic reserve was proposed according to the geological model of the failure of the debris flow material source.