The invention discloses an environmental-protection metal deoiling agent and a preparation method thereof. The metal deoiling agent is prepared by the following raw materials in parts by weight: 2-4 parts of sodium dodecyl benzene sulfonate, 4-6 parts of fatty alcohol-polyoxyethylene ether sodium sulfate, 2-3 parts of nonyl phenol alkylphenol polyoxyethylene ether, 3-5 parts of cocoanut fatty aciddiethanolamide, 1-2 parts of rhamnolipid, 1-2 parts of alkyl glycoside, 3-5 parts of zinc sulfate, 5-9 parts of sodium tripolysilicate, 4-7 parts of sodium citrate, 1-2 parts of benzotriazole, 2-4 parts of thiourea, and 2-3 parts of polydimethylsiloxane. The preparation method of the metal deoiling agent comprises the following steps: firstly, all surface active agents are compounded; and then, other auxiliaries in the formula are added for uniform stirring to prepare the metal deoiling agent. The metal deoiling agent is free of sulfonic acid and phosphoric acid, is environment-friendly, caneffectively prevent metal from rusting, and is excellent in dirt removing effect, few in generated foam and easy to clean; and the preparation method is simple, easy to obtain the raw materials and suitable for industrial application.