Due to its advantages of high output level and high output power quality, modular multilevel converter (MMC) is widely used in grid-connected inverter systems. In this paper, a feedforward current decoupling control strategy based on fractional order PIλ is proposed for MMC grid-connected control. This strategy further improves the dynamic performance and robustness of the system while satisfying the steady state performance of the system. The parameter design of the PIλ controller is mainly combined with the vector method and the ITAE criterion. Meanwhile, the improved Oustaloup approximation algorithm and the Tustin discretization method are used to realize digital application of the controller. By comparing the control effects of simulations and experiments using PIλ controller and PI controller which have demonstrated that the fractional order PIλ controller has better tracking performance, faster response speed, lower THD of grid-connected current, and better MMC grid-connected operation.