Abstract: Drying of the thin film coated on a particle surface is a basic step for spray-fluidized-bed drying. In this work, the relationship between the vapor pressure and the moisture content of the wet materials is analyzed and a physical model for the drying of the thin film coated on a particle surface is proposed to study the mechanism of spray-fluidized-bed drying.The numerical simulation is in good agreement with the experimental data.In addition, the effects of some particle parameters，such as density，specific heat，diameter，thermal conductivity，on the drying are discussed.The results can be used for the scale-up and optimal design of spray-fluidized-bed drier.