The invention discloses a unified power flow control system and method for urban rail transit photovoltaic energy-storage traction power supply. The system comprises a power adjustable device and a power adjustable device in a DC traction power supply network of an urban rail transit traction power supply system with photovoltaic energy storage power supply, power-adjustable device controller of each traction power substation participating into primary adjusting, a unified power flow controller participating into the secondary adjusting, an economic scheduling plan controller participating into the third adjusting, a traction power substation comprehensive automatic subsystem, a central comprehensive monitoring system, and a communication network. The adjusting on the traction power substation DC bus voltage by the local controller is realized, the optimal power flow distribution of the DC traction network is realized so that the traction network is minimum in power loss and minimum involtage fluctuation, the traction network voltage level is improved, so that the train current at each place can be provided by traction power substations at two sides as much as possible; the economic scheduling plan can determine the power output plans of the adjustable power devices at different time slots, and the pre-charging/discharging plane of the energy-storage device, and the photovoltaic energy storage can be efficiently utilized.