Biomass gasification was performed on a fluidized bed reactor with steam as gasifying agent. Two-stage gasification processes in a fluidized bed were adopted. This research aimed to determine the effects of reaction temperature and steam-to-biomass ratio (u) on exergy distribution, chemical exergy, physical exergy and exergy efficiency of the product gas, and residual ratio and exergy efficiency of the unreacted carbon, etc. Over the ranges of the test conditions used, chemical exergy varied from 10832.13kJ/kg to 16510.54kJ/kg, physical exergy ranged between 685.05kJ/kg and 1146.71kJ/kg chemical exergy/physical exergy ratio varied from 13.5 to 17.7, and exergy efficiency of product gas ranged between 35.52% and 60.78%. The results showed that the top two contributions of gas component to exergy value were H2 and CO. With the increase of reaction temperature, chemical exergy, physical exergy and exergy efficiency of the product gas increased, whilst chemical exergy/physical exergy ratio, and residual ratio and exergy efficiency of the unreacted carbon decreased correspondingly. The exergy value and efficiency of the product gas first increased and then decreased with the increase in u. An optimal value of u should be chosen between 1.2 and 1.6.