One cycle control has been widely used for active power filters (APF) because it has a simple structure, high precision, and fast response. One cycle control techniques mainly concentrate on parallel APF at present, but its application in series APF needs to be explored further. We introduced the one cycle control method to a direct current (DC) side series APF. By analyzing its working principle, mathematical models based on one cycle control theory were derived for the DC side series APF, and the control equations were established. Simulation results verify the correctness and reliability of the method proposed.