The invention provides a rust removing agent replacing hydrochloric acid to remove rust. The rust removing agent for removing the rust is prepared from the raw materials in parts by weight: 20-30 parts of composite organic acid, 5-10 parts of polymethylacrylic acid, 6-12 parts of chromium trioxide, 10-20 parts of a surface active agent, 3-6 parts of sodium gluconate, 1-3 parts of triethanolamine,1-3 parts of polyacrylamide, 1-2 parts of 1,4-butynediol, 0.01-0.1 part of sodium chloride, 0.5-2 parts of a functional additive and 70-90 parts of water; the pH value of the rust removing agent is about 6.0, and the density is 0.9-1.2 g / cm<3>; according to the rust removing agent, the hydrochloric acid is not used, that is, generation of acid mist is reduced from the source, matter which harms human body is not used in the rust removing agent, the environment cannot be polluted, and the rust removing agent is an environment-friendly rust removing agent; and the rust removing agent has a superior rust removing property, the rust removing time is short, meanwhile, the rust removing efficiency is high, the gloss on the surface of metal substrate effectively recovers, and the rust removing agent has good application prospects.