When traditional clustering algorithms are used to partition a network for reactive power/voltage control， there are shortcomings in scalability and it's difficult for the outcome of partition to guarantee that the controlled nodes and the corresponding reactive power source nodes are partitioned into the same area. A mapping-based partitioning algorithm for reactive power/voltage control is proposed. First of all， on the basis of the electrical distance， the cohesion of a hierarchical clustering algorithm is used to obtain the optimal number of areas and the area of reactive power source nodes. Then the mapping partition algorithm is used to determine the areas of the controlled nodes. Rather than depend on the state estimation， the method proposed is only based on real time network topology and parameters. The numerical results concerning on IEEE 39-bus， IEEE 118-bus system and Fujian Power Grid respectively show that the controlled nodes and reactive power source nodes that control them are mostly partitioned into the same area by using the algorithm proposed.