The invention relates to an aqueous ultra-thin expansion type steel structure fire-proof anti-corrosive paint and a preparation method thereof. The fire-proof anti-corrosive paint is prepared by adding ammonium polyphosphate, pentaerythritol, melamine, titanium white, expandable graphite, a preservative, a ceramic filler, an antifoaming agent, a dispersing agent, a plasticizer and the like into organic silicon-modified acrylic resin emulsion serving as a film forming base material. The paint has the advantages of high fire-proof performance, anti-corrosion and anti-rust function, and high water resistance, acid-alkali resistance and corrosion resistance, capability of meeting the requirements of various steel structures on the fire-proof and anti-corrosion performance, environmental friendliness, low cost, and readily available raw materials, so the paint can be widely applied to fire-proof protection of various steel structures.