Abstract: Aiming at the problems of unbalanced grid-connected voltage-current and power coupling that will be caused by the grid-connected inverter when the grid line impedance is unbalanced, this paper proposes a current closed-loop control strategy based on an improved proportional-integral quasi-resonant controller(QPIR). This method uses a static coordinate system so that there is basically no coupling between active and reactive power. In this paper, firstly, the control structure of LCL-type grid-connected inverter is established; secondly, the traditional proportional-integral and quasi-proportional-integral controllers are introduced, and the improved QPIR control strategy is proposed; lastly, the three control strategies are compared and analyzed in simulation. The simulation model is established by MATLAB/Simulink platform, and it is verified that the method not only improves the voltage unbalance, but also reduces the static error of the grid-connected power, and realize the decoupling control of active and reactive power.