Considering the salient pole and high magnetic nonlinearity of the electromagnetic doubly salient (EMDS) DC generator, a 12/8 pole prototype EMDS generator is designed and calculated using a 2-D finite element method (FEM). The phenomenon is analyzed and that the phase voltage wave changes between 120° and 180°. The influence of the exciting current and armature reaction on the DC voltage ripple of the generator is discussed in detail, and the nonlinear rules are gained that DC voltage ripple changes accordingly. The theoretical analysis is verified by the simulation and experimental results. The results are helpful for the optimal design of the generator and the optimal control of exciting-winding. We conclude that the filter-capacitance of the rectifier can be designed.