A phenomenological model describing the resuspension of polydisperse suspension in shear flow is presented. The model combines mechanisms of hindered sedimentation and shear-induced particle migration. The latter is expressed in terms of migration potentials for mono and polydisperse mixtures. The calculated results agree well with available experimental observations. It predicts the rise and location,of the suspension upper surface, the separation of species:in the suspension and the location and sharpness of interfaces between species. It can be used to analyze the flow of concentrated polydisperse suspensions under gravity in complex geometries and to predict macroscopic properties associated with these flows.