In order to solve the problem that the voltage of power grid can be too high when runs at low load period， two-stage online auxiliary decision-making method based on united generators leading-phase operation is proposed. The lower voltage limit of power plant and transient stability constraints are considered in the method. Firstly， based on the generator regulation sequence calculated by the integrated reactive power sensitivity index， using the heuristic method iteratively， auxiliary decision-making strategy is formed without considering the transient stability constrain. Then the transient stability of the initially selected strategy is checked. If the result shows unstable， seek the generators which need to lessen the regulation and its count based on generators factor of influence， and check again once only. By analyzing the checking result， the regulation strategy is gained which can partly solve the voltage problem. Case studies using a real power grid verified the effectiveness of proposed method.