Abstract: As an important channel for trans-regional transmission of Shanxi power grid,±800 kV Yanhuai DC undertakes the important tasks of new energy consumption and trans-regional power mutual supply.The power transmission capacity of Yanhuai DC is restricted by the low voltage and transient voltage rise of AC busbar at Yanmenguan converter station and the thermal stability of 500kV Huguan triple loop line.Its power transmission capacity is strongly coupled with the startup mode of supporting power supply.When the 500 kV AC line maintenance near Yanhuai DC is carried out,its transmission capacity is seriously weakened,which has adverse impacts on power supply guarantee and new energy consumption.In this paper,a scheme of installing safety control device under AC line maintenance mode to improve power transmission capacity is proposed,and the corresponding control strategy is put forward.