Different air distribution craft should impact the temperature of biomass gasifier in the gasification process. After temperature compared test, the bed temperature in the condition of double-layer air distribution is lower than the center tube air distribution. Using the fluid analysis software Fluent to simulate the pressure field under those two crafts, the result displayed that the pressure of pyrolysis layer of biomass gasifier bed in center tube air distribution was reduced, and the pressure field became more regular. The conclusion is the volatile in pyrolysis would be more precipitated if the pressure of this field was prompted based on the combustion theory, and the reaction rate and temperature would speed up and improve. That explained the result of gasification test by the perspective of bed pressure. Finally the accuracy of simulation result was tested by the method of error analysis.