Geomagnetic storms are violent disturbances of the geomagnetic field around the world, which produce geomagnetic induced currents(GIC) in power system. Power transformer enters the half-wave saturation state under the influence of GIC. The harmonics and reactive power loss produced by transformer affect the voltage stability of power system and cause the maloperation of relay protection devices in power system. With the increase of voltage level and the expansion of power grid scale, geomagnetic storms will seriously threaten the safe operation of power grid. Based on the analysis of the mechanism of magnetic storm disaster and the description of fault propagation and power system response, this paper deeply understands the influence of geomagnetic storm on power system and its electrical equipment. The prevention and control of secondary hazards of GIC is an important subject in the study of geomagnetic storms. This paper summarizes the research framework and ideas of the impact of magnetic storms on the voltage safety of power grid, combs the research results of the optimal control devices for suppressing DC bias of transformers. An optimized treatment of GIC is proposed which has obvious advantages compared with traditional methods.