A method for allocating VAR support cost based on branch's complex power components and reactive power value was presented. It is pointed out that sources' active power and loads' complex power are responsible for VAR support cost based on analysis. Based on reactive optimal power flow (OPF) solution considering reactive power value, each sources' active power and loads' complex power was modeled by each of their equivalent nodal injection current sources, and then each of sources' reactive power used for var support was modeled by a shunt reactance called “cost reactance”. Finally, the nonlinear relationship between cost resistance and equivalent injection current sources was found out on the basis of the algorithm of branch's complex power components. As a result, VAR support cost of each cost reactance was accurately allocated between sources' active power and load's complex power. Compared with the existing methods, this method is of the following properties:1) The VAR support cost of a power system is always recovered;2) It is applicable for any transmission systems of looped configurations and loop flows. It does not need any assumption and simplification, and takes into account the interaction between active and reactive power. The method proposed here gives a completely new analytical way to allocate VAR support cost. The results from the simulation of different power networks have shown that the proposed method is effective.