Abstract: Accelerating Rate Calorimeter (ARC) has been utilized to investigate biomass components and several types of biomass pyrolysis. The results showed that, pyrolysis under constant input power, cellulose had a exothermic peak in the range of 256.2-279.2 ℃ and generated heat 673.9 J/g. The residue yield was 51.8%. Xylan also had a sharp exothermic peak at 219.8-253.7 ℃, released heat 873.3 J/g. The residue yield was 68.7%. The heat flow curve of lignin pyrolysis showed a endothermic trend between 133.3-292.2 ℃ and absorbed heat 340.1 J/g. The residue yield was 80.4%. During biomass pyrolysis, two consequent exothermic peaks have been found in the heat flow curves. These two peaks are caused by hemicellulose and cellulose pyrolysis respectively. The endothermic trend of lignin has also been detected as well. Each biomass has released different amount of heat, but the initial heat releasing temperature is around 190 ℃. The first peak temperature is around 220 ℃ and the second peak is concentrated at around 255 ℃.