Abstract: The flow behavior of bottom discharge was studied in a fluidized bed using the computational particle fluid dynamic (CPFD) numerical method.The effect of discharging pipe diameters in a fluidized bed was obtained, and the detailed flow features were investigated.The calculation results showed that the fluidization behavior was influenced by discharging pipe, and the increasing pipe diameter would enlarged the affected area in fluidized bed.The solid flow rate increased with bed height, gas velocity and the square of pipe diameter.A correlation was derived based on the hydrodynamics of pseudo fluid, which could predict the variation tendency of bottom ash discharge.According to the distribution of the gradient of particle volume fraction in fluidized bed, there existed a vaulted critical plane above the openings of the air distributor, which divided the flow region into two parts with different flow behaviors of bottom ash discharge.