A modelling of a continuous fluidized-bed crystallizer is developed. The model is based on the description of the fluidized bed as a multistage crystallizer, in order to take into account the segregation and particles mixing within the bed. This model is compared to experimental data obtained during the laboratory-scale crystallization of tetrahydrate sodium perborate. It gives a better prediction of the mean size of the product than a usual model of suspended bed based on the assumption of perfect size classification. It can also predict the size distribution of the crystals along the column.