The utility model provides a railway purifies power supply unit, include: the soft way of charging, input transformer, the many level converter of chain, filter circuit and output transformer, the soft way of charging insert input transformer, input transformer take a percentage and insert the many level converter of chain, the many level converter of chain cascade by power unit and constitute, power unit by single -phasely do not control the flat ripples electric capacity of rectifier bridge, direct current energy storage, it is single -phase that control the H bridge and bypass contactor constitutes entirely, the filter circuit input insert many level converter's output, the other end inserts output transformer. The utility model discloses in using electric Railway, can keep apart the fluctuation and the harmonic interference that pull net 27.5kV voltage, export reliable and stable voltage, for station in the railway electric system interior, link up the line, self -imposed power line provides the power.