The invention relates to a steam action-based metal material surface modification method and a device therefor. The steam action-based metal material surface modification method is characterized in that according to chemical characteristics of reactions between H2O and a metal material such as Al, Mg and Ti, in the presence of saturated steam or superheated steam as an interaction medium, a functional film is in-situ synthesized on the surface of a base. The steam action-based metal material surface modification method has the obvious effects of water saving, emission reduction, environmental protection and high efficiency, utilizes water as main even only raw material, and has the advantages of zero involvement and zero discharge. The device comprises a steam generator, a steam distributor, a reaction tank, a liquid storage tank, a workpiece table and a driving motor and has the advantages of safety, reliability, simple structure, and use convenience. Through the steam action-based metal material surface modification method and the device therefor, in metal material surface modification, high-level treatment effects are obtained and potential damage produced by the prior art on the ecological environment and human health is eliminated thoroughly and cleaner production is realized really.