The invention discloses a steel-structure super-thin intumescent fire-retardant coating. The steel-structure super-thin intumescent fire-retardant coating is prepared from, by weight, 17-20 parts of ammonium polyphosphate, 10-15 parts of melamine, 6-10 parts of pentaerythritol, 6-12 parts of vinyl acetate-ethylene copolymer emulsion, 4-8 parts of thermoplastic acrylic resin, 5-10 parts of polyvinyl chloride resin, 3-7 parts of light calcium carbonate, 2.5-3.5 parts of methylcellulose, 18-26 parts of deionized water, 1-2 parts of thickening agent, 3.5-5.0 parts of dispersing agent and 0.1-0.3 part of antifoaming agent. According to the steel-structure super-thin intumescent fire-retardant coating, the technological process is simple, construction operation is convenient, total engineering cost is reduced, effective fire-retardant protection of a steel structure is achieved, and a decoration effect and a weather-resistant effect can be simultaneously achieved.