The invention provides a preparation method of solvent dilution type soft film antirust oil. The method comprises the steps that firstly, D60 solvent oil, lanolin magnesium soap, sulfonated lanolin calcium soap, dibutyl phthalate, sodium citrate, barium petroleum sulfonate, laurylene succinic acid, barium dinonylnaphthalene sulfonate, zinc naphthenate, beewax and trimethylolpropane triacylate are mixed, heating and heat-preserving stirring are conducted, and a first mixture is obtained; secondly, 3-mercaptopropionic acid and zinc acetylacetonate are added into glycol, diethylene glycol, polyglycerol fatty acid ester and silicone acrylic emulsion are added in sequence, heating and heat-preserving stirring are conducted, and a second mixture is obtained; lastly, the first mixture and the second mixture are mixed, an antifoaming agent, an antioxidant, a thixotropic agent and an antirust agent are added, and the mixture is stirred to be uniform. The antirust oil has good corrosion resistance, and the salt mist corrosion resisting time of a carbon steel 45 piston rod processed with QPQ for 2 h at the salt bath nitriding temperature of 570 DEG C can reach 817 h.