The dynamic stall process in three-dimensional (3D) cases on a rectangular wing undergoing a constant rate ramp-up motion is introduced to provide a qualitative analysis about the onset and development of the stall phenomenon. Based on the enhanced understanding of the mechanism of dynamic stalls, a 3D dynamic stall model is constructed with the emphasis of the onset, the growth, and the convection of the dynamic stall vortex on the 3D wing surface. The results show that this engineering dynamic stall model can simulate the 3D unsteady aerodynamic performance appropriately.