Sulfuric acid and nitric acid are two typical impurities in manufacturing, storage, processing, and transportation of nitrocellulose, and may reduce the thermal stability of nitrocellulose and increase hazards. Thermal behaviors of nitrocellulose contaminated by nitric acid and sulfuric acid were explored by a C80 micro calorimeter. Two exothermic processes were observed after adding acids into nitrocellulose. Kinetics and thermodynamics of pure nitrocellulose and its mixture with two acids were obtained by Kissinger method and Ozawa method. The catalytic mechanism was tested by analysis of reaction curve and isothermal experiments. Impurities of nitric acid and sulfuric acid decreased thermal stability of nitrocellulose with different mechanisms.