The invention discloses a direct current power source system of a transformer substation. The direct current power source system is composed of a high frequency switching power source charging module, a direct current power source monitor, a direct current bus, a capacitance battery pack and a feeder output module. The high frequency switching power source charging module is connected with an alternating current three-phase power source, the direct current bus and the direct current power source monitor and used for converting the alternating current into the direct current under the control of the direct current power source monitor, the direct current bus is connected with the capacitance battery pack and used for charging the capacitance battery pack, and the feeder output module is connected with the direct current bus and used for providing a power source for a load. According to the direct current power source system, the capacitance battery pack serves as a storage battery, due to the fact that capacitance batteries can be in floating charging and can also be in uniform charging for a long time, the requirement for the performance of a battery charger is not high, the consistency of the capacitance batteries is very good, the capacitance batteries can be connected in series into a set to be connected to the direct current power source bus, and the defects of a traditional lead-acid battery are well overcome.