In order to solve the problem that the capacity of line transformer in AC power network interconnected by conventional bus switch can not be utilized reasonably, a coordinated control strategy for active power of AC power grid on both sides was proposed, which relies on a new type of high-power flexible interconnection equipment composed of back-to-back voltage source converter. The topological structure and basic control principle of the flexible interconnection equipment were introduced, and a method of generating active power reference was developed to realize the reasonable capacity of the transformers on both sides of the line. Moreover, a simulation example was built based on PSCAD/EMTDC to verify the basic control of the flexible interconnection equipment and the proposed coordinated control method of active power cooperation. Simulation results show that when the flexible interconnection equipment adopts the proposed method, the cooperation of active power of AC lines on both sides can be realized, and the problem that the capacity of line transformer can not be allocated reasonably is solved.