Abstract: The contents of cellulose, hemicellulose and acid insoluble lignin were determined by NREL. The chemical composition of Pinus massoniana was analyzed under high temperature hydrothermal treatment. The results indicated that cellulose was decomposed at 160 ℃, the maximum decomposition of its content at 200 ℃. Hemicelluloses were decomposed at 140 ℃ due to the poor thermal stability which caused by branching structure and amorphous tissue. The content of acid insoluble lignin increased slightly with the prolongation of hydrolysis time. Temperature and time were significant factors affecting the content of 3 major elements in the high temperature hydrothermal treatment, and the influence of temperature was more significant.