Abstract: This paper studied the characteristics of geomorphology, fire behavior, unconsolidated source material volume, runoff and sediment production related to post-fire debris flow formations, field investigation in the burned area and rainfall simulation experiment were adopted to study the post-fire debris flow in Huayanzi gully, Mianning County, Sichuan Province occurred on 4 July 2019. The associated ash layer, water repellency and permeability experiments were also conducted. The results suggest that (1) the runoff charge shows a positive correlation with water repellency in burned area. (2) the sediment yields in severely burned area are conspicuously larger than that in moderate and slight burned areas. (3) the water repellency in burned area is approximately positively correlated with fire severity, while the permeability presents the negative correlation. This study revealed the evolution process of post-fire debris flow, and provided theoretical basis for the prevention and early warning of post-fire debris flows.