According to the requirements of relevant standards of power quality, the accuracy calibration under harmonic frequency must be superimposed with the rated fundamental wave. High-voltage voltage sources suitable for harmonic characteristic test of high-voltage transformers can only generate pure harmonics. Since the fundamental wave cannot be superimposed, it does not meet the requirements for harmonic characteristic test of voltage transformers of 110 kV voltage level. Therefore, this paper develops a voltage transformer harmonic test platform for 110 kV voltage level. In order to realize the boost function of harmonic superimposed fundamental, the harmonic transformer in this platform adopts the working principle of boosting the primary side of the wide frequency transformer and the industrial frequency transformer in series. Harmonic power supply and industrial frequency power supply input voltage signals from the secondary side of the broad-band transformer and industrial frequency transformer respectively. In addition, the distribution parameters in the equivalent circuit of the transformer will resonate in series or in parallel with the change of capacitive reactance and inductive reactance when the frequency changes. The harmonic step-up coils of this platform use a “strand winding” technique between the high and low voltage coils to control the distribution parameters. Amorphous alloy material is chosen for the core of the harmonic boost coil. The harmonic boost coil is optimized from various angles to reduce the risk of resonance. Subsequently, this paper carries out a harmonic characterization test based on the developed platform. The test results are compared and analyzed with the theoretical calculation data. It is verified that the performance of the test platform meets the harmonic characteristic test requirements of voltage transformers of 110 kV voltage level.