To solve the problem that transient overvoltage of AC system will lead to the wind turbine generator（WTG）overvoltage tripping in DC near area under the mono-polar block fault

the influence mechanism of mono-polar block on transient overvoltage is analyzed

and it is pointed out that the excessive reactive power of AC system is the fundamental cause of the transient overvoltage. The characteristics of sound pole under mono-polar block fault are analyzed;in the meantime

by taking the balance state of reactive power at sending bus as regulation target

the expression of DC current command value of sound pole is derived

and the DC control strategy to suppress transient overvoltage is proposed. When the transient overvoltage can not be completely suppressed

under this improved control strategy

a coordinated control strategy is proposed to further suppress the transient overvoltage by putting into a reasonable capacity to avoid the WTG overvoltage tripping. Finally

the improved CIGRE HVDC bipolar standard system and TZ HVDC transmission system are set up on the DIgSILENT simulation platform. It is verified that the strategy can effectively block the transmission of transient overvoltage and inhibit the large-scale WTG overvoltage tripping.