Abstract: To ensure the stability of the transmission voltage and effectively control the operation of the DC transmission system in the event of three-phase short circuit fault,this paper proposes a DC transmission system operation control method based on the multilevel converter module（MMC）. The multilevel converter module is designed by using the anti parallel diode and parallel capacitor to obtain the AC equivalent inductance to ensure that the AC/DC flow of the converter station is the same as the active power,and clarify the power situation inside the converter station. The module is combined with the feedforward decoupling compensation term,and the PI is used to obtain the input value of the current inner loop operation controller to realize current decoupling, and increase the stability control of DC voltage,and improve the anti-interference of the transmission system. The corresponding reference value is obtained through the correction and control link,and the optimal operation control result is obtained. The experiment proves that the designed module can ensure the smooth operation of the power transmission system under normal working conditions,control the impact in a safe range when a fault occurs,and ensure the stability of the power transmission system.