In this paper, an improved H7 inverter topology for leakage current suppression is proposed to suppress the leakage current in the transformerless photovoltaic power generation system. Based on the topology of H7 inverter, a clamping circuit is added. The circuit is composed of three voltage divider capacitors with equal capacitance and three clamping switches. The clamping circuit can keep the common mode voltage of the inverter stable in the freewheeling state. At the same time, a high-frequency control scheme of common mode voltage is proposed, which increases the frequency of common mode voltage and the common mode loop impedance on the basis of the ensuring that the voltage of clamp point is U_PV/3 or 2U_PV/3. The common mode characteristics of the system is optimized and the leakage current suppression effect is better. A prototype with 200 W output per phase is built, and the correctness of the theoretical analysis is verified by saber simulation and hardware experiment.