The invention discloses a biodegradable metal rust inhibitor. The biodegradable metal rust inhibitor is prepared from styrene acrylic emulsion, modified filler, a modified reinforcing agent, modified anti-rust reinforcing agent, methyl methacrylate, butyl acrylate, ammonium persulfate, styrene, ethyl acrylate, epoxy resin, epoxy acrylic resin, benzotriazole, zinc dialkyl dithiophosphate, sodium tripolyphosphate, naphthenic base oil, diethylene glycol propyl ether, octadecylamine, alkyl sodium sulfonate, sulfamic acid, hexamine, barium alkylsulfonate, thia fatty acid ester, fatty alcohol-polyoxyethylene ether, propenyl alcohol amine, sodium carboxymethyl starch, arabic gum, maleic-methyl acrylate copolymer, potassium dihydrogen sulfate and sodium molybdate. The metal rust inhibitor has excellent anti-rust performance and can be degraded.