Invention relates to the field of corrosion protection of metals, in particular steel, which are operated in corrosive environments. Multifunctional steel corrosion inhibitor contains trialkoxysilane or substituted trialkoxysilane and additionally a plant extract obtained from waste plant material by the extractant system water-isopropyl alcohol-ethyl alcohol of moderate polarity. Technical result: effective anti-corrosion protection, irreversibility of inhibitor adsorption in various corrosive environments and the effect of protective aftereffect of inhibitors.