Abstract: The difference of pyrolysis characteristic among cellulose, xylan and lignin was studied by TG and heat radiation reactor. Xylan has a lower thermal stability than cellulose, and decomposes at 217℃~390℃. Cellulose has a higher onset temperature of pyrolysis and lower yield of char compared with xylan and lignin, and decomposes in a rather narrow temperature range. Lignin decomposes over a broad temperature range from 227℃ to 550℃ with a char yield of 42% which is the highest of the three fractions. The trend of biooil yield from the three components with temperature is the same, which increases firstly and then decreases. The biooil yield from cellulose is the highest of the three fractions, but it is lest stable. The biooil from xylan and lignin shows a higher thermal stability. The char yield for cellulose, xylan and lignin decreases with temperature rise, and finally closes to a constant value about 1.5%, 22% and 26%. The gas yield increases with temperature rise, but the contents of the gas are different according to the different fraction.