Debris flow is a high frequency geological disaster in mountainous areas. The occurrence of debris flow on the left bank of the Panda Sea in Jiuzhaigou Gully caused huge losses to the scenic area. Based on the field investigation, the bulk density, peak flow, and average velocity of the debris flow were calculated with field experiments and theoretical formulas. The formation mechanism of the debris flow on the left bank of the Panda Sea in Jiuzhaigou Gully was analyzed. Massflow was used to simulate the movement characteristics of the debris flow. Based on the status of current material source, water source, and topography of the gully, the analysis results show that the gully is likely to have a larger debris flow again, so two control measures for the impending debris flow in this gully are proposed.