Due to the complex optimization strategy and long computation of the traditional reactive power optimization, it is still difficult to apply to real-time optimization control for power grid, this paper proposes a simple and rapid idea of voltage optimization based on fuzzy membership and interval power flow algorithm. At first, it obtains the corresponding interval voltage by the interval control variable provided by the grid and intersecting with the security voltage interval to get feasible voltage range. Then it finds the voltage of maximal membership during this interval as known quantity to solve the power flow and require the optimal control variable combinations. Comparing to the traditional intelligent algorithms, the results of the algorithm is suitable for the voltage optimization in provincial power grid AVC system as a fast and efficient optimization method.