The effects of particles projection from a fluidized bed surface on the heat and mass transfer between two isothermal regions was investigated through experiment and mathematical modelling. The amount of particles projection increased with the increase of superficial velocity and the increase of the bed height. The amount of particles projection between the two regions was 50%-65% of the total amount of the mass transfer in the bed. On the basis of the Rong-Fan shallow bed mathematical model and experimental conditions

a dynamic model was proposed. The "On Line Method" derived by R. F. Sincover and N. K. Madson was used to solve the partial differentia] equations. The calculated results were in better agreement with the ex-perimental values.