A method for producing hydrogen by using magnesium scrap is provided. First, adhering the melting magnesium scrap to platinum-coating titanium meshes, and putting the adhered meshes in an airtight reaction chamber, which is loaded with sodium chloride solution, to carry out a spontaneously hydrogen producing reaction. The gas produced by the reaction is then conducted to a low temperature exsiccator for condensing the vapor involved in the gas. Next, the gas is collected by a collector immediately. The apparatus comprises a sodium chloride solution container, an airtight reaction chamber, a low temperature exsiccator, and a gas collector. Ducts connect with each component and control the gas/solution pass in and out by using valves.