With Larix gmelinii forests as test objects in Tahe Forestry Bureau on Great Xing’an Mountains, northeastern China, taking the investigation of forests burned at different time, their roots were sampled to analyze the change of root biomass, C and N nutrient concentration and C/N value after the fire. The results showed that: 1) One week after fire, live root biomass of low intensity and moderate intensity burning trees were only 80% and 36% of control trees, fine root biomass of ＜1 mm diameter were 60% and 19% of control trees, respectively; 2) Three months after fire, fine roots of low intensity burning trees had came to a certain degree of recovery, fine roots of moderate intensity burning trees was significantly lower than the recovery degree of low intensity one. Two years after fire, there was no significant difference between the root biomass of low intensity burning tree and control, and there was no significant difference between fine root biomass of ＜1 mm diameter of moderate intensity burning trees and control; 3) Fire reduced tree root nutrient concentrations of carbon and nitrogen, low intensity burning decreased the value of C/N, however, moderate intensity burning increased the value of C/N. Forest fire had a significant impact on tree roots. After roots of trees were burned, their physical activity and living environment were also changed and many factors will affect the recovery of roots.