This paper proposes a modular multilevel hybrid active bridge (MHAB) DC-DC converter, which is suitable for medium-voltage DC distribution grid. A modular structure and a conventional two-level half-bridge are employed in the medium-voltage (MV) and low-voltage (LV) sides of the proposed converter respectively, which is suitable for MV DC distribution grid, such as ±10 kV to 400 V. The system structure is analyzed and simplified. The pulse-width modulation (PWM) plus phase shift (PS) control strategy is applied to control the transferred power, and submodule DC-link capacitor voltage sorting method is adopted to balance the MV side submodule capacitor voltages. The effectiveness of the proposed MHAB converter is verified by simulation results.