Abstract: The armature reaction and commutation overlap are two major factors which influence the external characteristics of the electromagnetic doubly salient brushless DC generator.In this paper,the effect of armature reaction and commutation overlap on electromagnetic doubly salient brushless DC generator’s external characteristic were discussed.Using the finite element analysis（FEA）,series waveforms of the half-wave rectifier with single-phase,the three-phase independent half-wave rectifier and the switched reluctance generation mode were analyzed and compared.Experiments on the prototype verify the correctness of the analysis.Analysis results show that,the increasing magnetic properties of the switched reluctance generation mode helps to decrease the excitation power.The demagnetization effect caused by the mutual inductance can be ignored because the mutual inductance vales is very small.The commutation overlap is the important factor which causes the switched reluctance generation mode’s external characteristic softened,and to reduce the effect of commutation overlap on the doubly salient power generation system should be one effective optimization approach.