Along with the increasing use of cables in power grid and the increasing ration of distributed power sources’ synchronization, such as small hydropower’s synchronization, increasing the reactive power transmission on the line, make it difficult to achieve the balance of reactive hierarchical partition. Take a certain region’s power grid for actual examples, after the installation of magnetic control reactor (MCR), using immune genetic algorithm (IGA) to coordinate the capacity of magnetic control reactor and the existing reactive power resources, the results show that the magnetic control reactor does much good to absorb the system’s excessive reactive power and limit the voltage’s increasing.