Aiming at the leakage current problem in the transformerless photovoltaic grid-connected system, a symmetric DC bus switch transformerless current source photovoltaic inverter is proposed. The topology and switch configurations of main circuit of the inverter are given in this paper, and then generation mechanism and suppression mechanism of the leakage current are analyzed by establishing common-mode equivalent circuit model of the parasitic capacitance of the photovoltaic modules. According to the switch configurations and the suppression analysis, the corresponding unipolar dual-carrier modulation strategy and quasi-PR control strategy are designed. Simulation and experimental results show that the proposed converter has good leakage current suppression capability.