Abstract: Y-type modular multilevel converter (Y-MMC) is a kind of three-phase AC-AC converter with high power, low cost and high voltage characteristics, which can be applied to the field of offshore wind power. At present, the low frequency and power frequency current of Y-MMC are generally controlled by PI strategy, whereas the control effect of PI strategy for Y-MMC is not ideal. Therefore, a differential flatness control strategy of Y-MMC low frequency side and power frequency side current is proposed to solve this problem. Firstly, the decoupling model of Y-MMC is derived according to its topological structure. Then, the mathematical expressions of positive- and negative-order PI control strategy and positive-and negative-order differential flatness control strategy are derived, and the global asymptotic stability is proved by the Lyapunov theory. Finally, the simulation and experimental results on Matlab/Simulink simulation platform and RT-LAB semi-physical platform show that the proposed differential flatness control method(strategy) is correct and effective.