In order to determine the caloric requirement of biomass pyrolysis, simultaneous thermal analyzer was used for experiments of wheat straw pyrolysis. Powder biomass sample about 5 mg was put into Platinum crucible with lid on a high accuracy DSC-cp sample holder in the furnace. And then the sample was heated from ambient temperature up to the maximum temperature of 973 K at the heating rate of 10 K/min. The product gases were swept away by 25N mL/min Nitrogen. Mass change and calorimetric effects were recorded and analyzed. The process was investigated in detail through the comparison of DTG (differential thermal gravimetry)and DSC (differential scanning calorimetry) curves. And after the water influence in the DSC curve was eliminated, the relationship between caloric requirement and the temperature of the dry wheat straw was obtained by integrating the DSC curve. Result showed that 523 kJ, 558 kJ, 592.0 kJ were required respectively to make the temperature of 1 kg dry wheat straw raise from 303 K to 673 K,773 K, 873 K.