Z source inverter (ZSI) and its derivative topologies are widely used in photovoltaic (PV) field. In the non-isolated pv grid-connected system, the common mode voltage (CMV) changes over time, resulting in high-frequency leakage current flowing through the stray capacitance of the PV panels. By analyzing the CMV of ZSI, this paper proposes a simple method to reduce the CMV harmonics in ZSI. This method is realized by changing the state of the switch and by modulating the Fourier transform (MFT), the CMV of this method is compared with the CMV in the traditional ZSI in frequency domain. The The reference value of this method are verified through the simulation of a lkW ZSI.