The common mode current in non-isolated photovoltaic grid-connected inverter is analyzed from the point of view of safety regulation and decomposed into leakage current and residual current. A common mode voltage loop analysis model is established based on full bridge and influential factors and features of leakage current and residual current are researched. A method based on coordinate transformation is proposed according to their features. At the same time, virtual vertical signals need to be constructed for the method, so a kind of SOGI-QSG is introduced to process the signals. Experimental results show that the method can accurately calculate the value of each component and adapt to different grid frequencies automatically, so it has promoted value.