Abstract: As a typical source of debris flow after fire, the start of shallow surface landslides is inseparable from the change in root characteristics of fired land. In order to study the effect of root system changes on soil mechanical properties after forest fire, this paper mainly compares the soil root characteristics and shear strength of the burned areas with those of the non-burned areas in Zhengdou Township in Xiangcheng County of Sichuan Province, and conducts indoor single-strength tensile test and root-soil composite direct shear test. The purpose of this work is to investigate the deterioration of soil root characteristics and its effect on soil shear strength in the burned areas. The experimental results show that the forest fire reduced the number of roots, root diameter, root mass density and root length density in the superficial soil by 23.15%, 51.35%, 62.98% and 29.10%, respectively. The tensile strength of single root increased with the increasing root diameter, while the tensile strength decreased with the increasing root diameter. Under the condition of the same root diameter, the soil tensile strength and tensile strength decreased after fire. The shear strength of the soil in the burned area is obviously lower than that in the unburned area. The cohesion decrease derived from root weakening should account for this phenomenon. The obtained results may be useful in the study of the formation mechanism of shallow surface landslide in burned areas.