Al-Mg alloy is resistant to corrosion and oxide, and moreover, has decorativeness and machinability. All these make it an ideal material to protect. Due to light weight and high hydrogen storage, it has shown good perspective of application as a hydrogen storage material. To obtain good Al-Mg alloy, pure alloys of ultrafine structure need to be prepared. When preparing the alloys which are highly pure, electrodeposition is one of effective ways. At room temperature, the microstructures and components of alloys can be controlled by adjusting deposition parameters, which will lead to preparation of the alloys that is highly pure and ultrafine. In this paper, the effect of some factors on composition of Al-Mg alloy, morphology, and crystalline structure will be reviewed, such as electrolyte composition, current density, deposition methods, ways by which Mg ion is used, and experimental environment and conditions. Especially, the factors are mainly introduced when Mg-Al alloy is prepared at room temperature as well as application of Mg-Al alloy in decoration, resistant to corrosion, and hydrogen storage. Finally, the problems and future trends are presented when Mg-Al alloy is prepared at room temperature.