Abstract: In straw fluidized bed boiler，fluidization characteristics of straw particles have important effects on combustion efficiency，agglomerating behaviors and fouling.ANSYS FLUENT was used for simulation of flow of straw particles in fluidized bed，and effects of particle diameter on minimum fluidization velocity，particle velocity field and average volume fraction were analyzed.Results indicated that minimum fluidization velocity had a linear relationship with particle diameter. After reached fluidization state，bed′s pressure drop did not change with particle diameter.With increase of particle diameter，bed height of fluidized bed decreased and volume fraction of solid phase increased，also bubble diameter increased，and surface fluctuation caused by bubble burst increased.Simulation results could provide guidance for optimal design and operation of straw fluidized bed boiler.