In order to improve the robust and dynamic performance of T-type three-level converter and reduce the harmonic content of grid-side current, a new double closed-loop control strategy based on differential flatness theory and sliding mode control (SMC) is proposed. The SMC is adopted in the inner loop, and differential flatness control(DFC) is adopted in the outer loop. In this paper, the working principle of T-type three-level converter is analyzed, and the detailed steps of controller design are given. Finally, the feasibility and superiority of the control strategy are verified by simulation.