Regularities of delta formation processes at river mouths are considered. Hydrological-morphological model of delta formation has been worked out. The model includes four units. The first unit considers process of sediment accumulation due to decrease of velocities in river flow, the second one deal with sediment balance at river mouth and the mouth cone formation. The third unit describes vertical changes of the channel within a delta; the fourth one describes interconnected processes of delta network dynamics and redistribution of water and sediment discharges between delta branches.