This paper proposes a high-efficiency control method for an insulated DC-DC converter with a phase-shift inverter for a single-phase grid-connected photovoltaic generation system. The proposed control method for the inverter output power is regulated by controlling each phase angle of the inverter leg and by controlling the frequency. Moreover, the inverter switching frequency is controlled by changing the input current of the main circuit, and soft-switching can be realized by controlling the frequency. The phase angle of the inverter is controlled by the output voltage of the main circuit. The validity of the proposed method is confirmed via the experimental results. Using the proposed method, we find the efficiency that improved by a maximum of 3.6% as compared with the case of the conventional method.