The authors propose and investigate a new improvement method for transient stability under power line fault condition for commercial scale open cycle subsonic inflow disk MHD generators connected to the power system through time dependent numerical simulations of a total interconnecting system. The method needs no additional device and only manipulates the inverter control angle. Its control sequence has two steps. At first, the control angle is reduced toward 90degrees just after the fault occurs. Next, it Is linearly increased to its rated value with constant increasing rate per cycle after the removed line is reconnected. It is made clear through the simulations that the proposed control scheme of the inverter is very effective to improve the transient stability of the generator. The reduction of the inverter control angle is effective to stabilize the MHD generator, but the operating state shifts from its normal operation. The increase of the control angle can stably return the generator to its normal operation.