By integrating a ant colony optimization algorithm (ACO) with an interior point method (IPM)， a hybrid strategy for the optimal reactive power flow (ORPF) problem is proposed．First，the original ORPF problem is converted to a continuous non-linear programming problem by relaxing the discrete variables，and the initial solution is obtained by the IPM．Then according to the discrete feature of the control variables，the original ORPF problem is decomposed into a continuous optimization sub-problem and a discrete optimization sub-problem，which are solved by IPM and ACO respectively．By solving the two sub-problems alternately，the optimal solution of the ORPF problem can be obtained．IPM and GA take advantage of each other，so that the efficiency of the hybrid strategy is greatly improved．Furthemore，the numerical example of IEEE 30-bus and IEEE 118-bus system is employed to validate correctness and effectiveness of the proposed algorithm, and the result based on this algorithm is compared with that based on conventional discretization algorithm．