The utility model discloses a power frequency resonance step-up power supply for verifying a 550kV GIS internal voltage transformer, and the power supply comprises a voltage regulator T, an exciting transformer B, and a multi-combination electric reactor. The output end of the voltage regulator T is connected to a primary side of the exciting transformer B, wherein one end of the secondary side of the exciting transformer B is grounded, and the other end of the secondary side of the exciting transformer B is connected to the input end of the multi-combination electric reactor. The multi-combination electric reactor comprises at least one group of adjustable electric reactors. The beneficial effects of the utility model lie in that the resonance electric reactor is formed by the combination of a small-size fixed electric reactor and an adjustable electric reactor, thereby reducing the size and weight of equipment; the power supply is especially suitable for an on-site error verification, and improves the error verification level and efficiency of a large-size GIS internal voltage transformer.