The invention discloses a preparation method for anti-carbon deposition layer on the surface of a steel material part of an engine. The preparation method comprises the following steps of: surface leveling, cleaning treatment, chemical polishing, chemical decomposition deposition Si membrane, and oxidation treatment. Technological parameters such as temperature, pressure, flow, heat preservation time and the like are adjusted; a diffusion and penetration process of Si and O elements is controlled; compositions and structures of the surface layer of the material and the bounding force between the surface layer of the material and a substrate are changed so as to obtain a compact, adhesive, structure-controlled FeSi/Si/SiO2 coating; and a FeSi/Si/SiO2 gradient transitional composite membrane is obtained on the surface of the steel material part of the engine. The composite membrane has strong bonding force with the substrate, compact organization, small internal stress and smooth inertness, has characteristics of toughness, high-temperature resistance, corrosion resistance, bonding resistance and the like, endows the material with new surface characteristics, prevents the metal from directly contacting with organic matters, prevents the adhesion and deposition of organic colloidal materials and improves anti-carbon deposition performances.