Abstract: The short circuit current rises sharply after the DC-link fault of the modular multilevel converter (MMC), which seriously affects the safety of the DC grid. In this paper, a submodule two-stage active control (STAC) is proposed for this issue. According to the two-stage fault detection criterion and the preset maximum short-circuit current, the piecewise function K of the direct current is constructed, which output decides to reduce the proportional coefficient of the cast sub-mode to reduce the DC voltage and suppress the short-circuit current. In addition, the control parameters of MMC converter which under various conditions are designed for economize the cost of current limiting control strategy. The STAC does not affect the normal operation of the system and it can maintain power transmission during current limiting. Finally, the current limiting effect and performance of STAC are simulated and analyzed in the four-terminal DC grid. The results show that the current limiting method proposed in this paper effectively suppresses the fault current. The fault current flowing through the DC circuit breaker is reduced by 49.7%, the peak current of the bridge arm is reduced by 23.15%, and the DC voltage is restored 100ms after the fault.