In order to control the output power of a switched reluctance generator(SRG) at a con-stant speed, the output power of SRG is theoretically analyzed by using freewheeling control. First, through a theoretical analysis, a finite element simulation and an experiment, it was verified that the output power of SRG cannot be improved by using freewheeling control with a single pulse con-trol method(SPCM). Then, the maximum output power can be obtained by optimizing the turn off angles of SPCM at a constant speed, and at the same time, the formula of the optimal turn-off angle was presented, which meets the criterion for the output power maximization. Finally, numer-ical simulation and experimental results demonstrated the validity of the theoretical analysis.