Abstract: Through field measurement and laboratory measurement, the difference of height of lowest branch of tree and fire behavior before and after forest tending was compared, and the possibility of potential canopy fire before and after forest tending was quantitatively analyzed, which provided a basis for quantitative evaluation of forest tending effect. Five compartments were selected in Yunnan Forest Nature Center, and different forest tending methods were adopted to regulate and control forest fuel according to the distribution of forest fuel. The heat yield, fire intensity, fire spreading speed and flame height of surface fuel before and after forest tending were calculated by investigating the height of lowest branch and fuel load of 39 small classes in 5 compartments before and after forest tending. Through comparative analysis, the results showed that: 1) the average height of lowest branch of Cypress forest and Pinus armandii forest was 0.30 m and 1.43 m, respectively, and the simulated surface flame height was 0.34 m and 0.67 m, respectively. Pretending Cypress forest and Pinus armandii forest had a great canopy fire hazard. 2) The average height of lowest branch of Cypress forest after forest tending was about 1.50 m, and the distance between the surface flame was increased from-0.04 m to 1.34 m, which significantly reduced the hidden danger of high intensity canopy fire. 3) The average height of lowest branch of Pinus armandii forest after forest tending was about 2.02 m, and the distance between the surface flame was increased to 1.68 m, and the hidden danger of high intensity canopy fire was greatly reduced. Forest tending could effectively reduce the surface fuel load and increase the height of lowest branch, thus effectively reducing the possibility of crown fire.