A novel model for the sedimentation of polydisperse suspensions has been submitted. In the developed model of gravitational sedimentation, an attempt was made to take into account the main known physical features of the process, and a simplified calculation method based on this model has been proposed too. The approach novelty lies in that generalization of the sedimentation model for the case when a polydisperse suspension is specified not as a discrete set of fractions, but with the help of a continuous size distribution function of disperse phase particles, is proposed to do on the basis of a diffusion type equation, supplemented with source terms. Such a model also allows for taking into account the possibility of aggregation of different fractions during sedimentation. A developed model makes it possible to calculate the temporal evolution of the density of the settling suspension, as well as the evolution of the position of sedimentation front and the sediment surface along the reservoir height. The expression for the settling front evolution, which is of fundamental importance for the method of calculating the sedimentation kinetics of polydisperse suspensions, has been obtained.