The paper presents a novel continuously adjustable Peterson coil. If it is used in the system of neutral point grounding through Peterson coil, not only the high price can be reduced and the complicated problems can be solved of which the high voltage inductance controlling systems, but also advantages of the system of neutral point grounding though Peterson coil can be shown. It is introduces that how adopts low voltage thyristors for continuing adjusting inductance of the Peterson coil of which the voltage level ranges from 6 kV to 66 kV. This paper discusses the formula of calculating the inductance variable ranges and the harmonic currents which presents stable harmonic current under the phase controlled mode also. The theory of the designing coil is verified by the Saber simulation and practicality experiment.