The invention discloses aqueous fire-proof corrosion-proof paint for a steel structure and a preparation method thereof, and belongs to the technical field of paint. The aqueous fire-proof corrosion-proof paint comprises, by mass, 20-45% of a composite emulsion, 12-25% of a charring catalyst, 6-12% of a foaming agent, 8-17% of a charring agent, 5-10% of a fire retardant, 1-5% of layered double hydroxide, 8-18% of an corrosion-proof filling material, 4-12% of a strengthening filling material, 1-5% of modified nano-powder, 0.5-6% of an assistant and 10-30% of water. Through use of the composite modified emulsion as a base material, coating flame resistance, corrosion resistance and decorativeness are obtained and coating defects caused by a single emulsion as a base material are overcome. Through use of a small amount of the nano-powder, the coating is compact because of filling effects of the nano-powder, the coating corrosion caused by O2, H2O and Cl <-> is avoided, good fire-proof and corrosion-proof effects are obtained under the condition of a small addition amount and a cost is reduced. The aqueous fire-proof corrosion-proof paint has the characteristics of green environmental protection and simple preparation processes.