The invention discloses metal rust removing liquid and a preparation method thereof. The metal rust removing liquid comprises hexamethylenetetramine, triethanolamine, fatty alcohol-polyoxyethylene ether, sodium ethoxylated alkyl sulfate, polyethylene glycol, polyoxyethylene lauryl ether, triethanolamine oleate, sodium carboxymethylcellulose, lecithin and water. The preparation method comprises thesteps that the hexamethylenetetramine, the triethanolamine, the fatty alcohol-polyoxyethylene ether, the sodium ethoxylated alkyl sulfate, the polyethylene glycol and the sodium carboxymethylcellulose are dispersed in water, heating and stirring are carried out to achieve uniform dispersion, the polyoxyethylene lauryl ether, the triethanolamine oleate and the lecithin are added into the mixture,and after stirring and mixing, the metal rust removing liquid is obtained. The metal rust removing liquid is gentle in characteristics, and rust removing is easy and rapid.