Continuous co-phase traction power system is an effective method to eliminate neutral sections and provide high quality power for both the public grid and the catenary. The substations have the ability to provide cooperative support to each other to reduce capacity and improve system reliability. A fast power control method for substations is needed due to rapid load changes and low overload capability of the system. This paper proposes a fast power control method based on high-speed communication between substations, with additional transient power control to significantly improve the dynamic response of the system.