Hydrogen, as a future energy source, is thought as an alternative of fossil fuel in view of environment and energy security. Hydrogen has the properties of both fuel and electricity so that it can make the energy paradigm shift in the future. Therefore, researches on hydrogen in power system area are essential and urgent due to their huge effects on current paradigm. In this paper, the visions and technical challenges of hydrogen in power system are reviewed as energy storage, dispersed generation (DG), DC generator, and combined heat and power (CHP).