Hydrogen embrittlement is the consequence of strong interaction between hydrogen and metals and the cause of fracture failure of metal components. The mechanism of hydrogen embrittlement is reviewed and the harmful effect of hydrogen on metal is elaborated. The effect of hydrogen on the microstructure of metal is also introduced, thus refining the microstructure, purifying the melt, plasticizing and non-crystallizing. The proper use of hydrogen can prepare materials with better and special properties, improve processing conditions and simplify process. Meanwhile, the adsorption, diffusion and precipitation of hydrogen in metal and metal films can also help the purification of low purity hydrogen.