Abstract: When the flexible grounding device is used to solve the problem of three-phase unbalanced overvoltage in the distribution network, the common current control method depends on the accurate measurement of phase-to-ground insulation parameters and harmonic current, so it is difficult to be applicated. To this end, the difference between voltage control and current control of unbalanced overvoltage suppression method is studied. An unbalanced overvoltage suppression method based on zero-sequence voltage is designed. The control strategy of inner loop proportional-integral（PI） plus outer loop first-order inertial link is adopted based on double closed-loop control. This method realizes unbalanced overvoltage suppression without measuring the phase-toground insulation parameters and harmonic current, and further improves the performance. Simulation results verify the dynamic and steady-state performance of the proposed method, and show that the unbalanced overvoltage could be suppressed quickly and precisely under various conditions.