By analyzing the topology of modular multilevel converters（MMCs），an arm current direct control scheme for MMCs is presented to independently control the current through the upper or lower arm of an MMC.The small signal transfer function model of an MMC is built to analyze and design the feedback control scheme of arm current.Taking the grid-connected MMC inverter as an example and combined with the capacitor voltage balance control strategy，a comprehensive control scheme based on the arm current inner loop control is proposed to perform the grid current control as well as capacitor voltage balancing of an MMC.Simulation results show that the proposed arm current direct control scheme of MMC has excellent stead-state and dynamic characteristics;and it can effectively eliminate the three-phase inner circulating currents.The results clearly verified the feasibility and effectiveness of the proposed scheme.