In the field of electrified railways, a unified energy storage and transformation control system is proposed based on railway static power conditioner and supercapacitor energy storage system. In order to enhance the regenerative braking energy utilization, while improving power quality. Firstly, the parameters design of the supercapacitor energy storage system are given. Then, the working area of the system is divided into different parts under different working conditions. Meanwhile, the power allocation strategies among the two power arms and energy storage system in each of the parts are presented in details. Furthermore, the coordination control strategies which include instruction current or power detecting calculation and the control strategies of converters for both railway static power conditioner included and supercapacitor energy storage system are presented in each of the parts. Finally, the simulation under diverse working conditions has verified that the coordination control strategies. The system can not only realize the storage and utilization of regenerative braking energy including peak load shifting, but also can solve the power quality problems in electrified railways.