During the grounding fault of the line connecting the transformer and the inverter valve， a huge fault current will flow through valve group after setting by-pass-pair（BPP） within the fault clearing actions. The current value and direction of valve group are analyzed for this fault case. Over-current of valve group with setting BPP and without setting BPP are compared. This paper proposes an optimal fault clearing action for this grounding fault. This optimal fault clearing action can be used to avoid the huge over-current passing through the valve group during fault clearing process. It also helps to avoid valve group damage in the fault clearing process.