In this paper, a fractional-order control strategy of grid-connected inverter based on modified particle swarm optimization (MPSO) algorithm is proposed to improve the quality of grid-connected current. Firstly, the influence of integral order λ, differential order μ of fractional-order PIλDμ controller on the dynamic and steady performance of the controlled system is analyzed. Secondly, the fractional order PIλDμ controller is combined with current dual-closed-loop and voltage feed-forward control, then a current control strategy of grid-connected inverter based on fractional-order PIλDμ controller is proposed and compared with the traditional integer-order PID control strategy; Finally, the parameter range of fractional order PIλDμ controller is analyzed in detail, and the MPSO algorithm is used to optimize the parameters. The simulation results show that the fractional-order PIλDμ control system enhances the flexibility of the control system, reduces the total harmonic distortion rate of the grid connected current, and improves the stability and dynamic performance of the system.