Abstract: Based on integral modeling method，FLUENT software was used to simulate fluidized bed jet mill to explore the changes in internal flow field under different actuating medium. Simulation results showed that there is little difference in air flow velocity pressure with different actuating medium，while a higher outlet velocity can be obtained when actuating medium with lower molecular weight flow through the Laval nozzle. Meanwhile，higher velocity of injective air in grinding chamber provides more chance for particles to enter the axial velocity area. Therefore，an actuating medium with lower molecular weight can increase the grinding efficiency effectively. Simulation results for different inlet pressure and back pressure on grinding airflow showed that the airflow velocity increases obviously with the building up in the inlet pressure，but less effected by the building up in the back pressure .