The invention provides an oil stain-resistant and antirust water-based modified acrylic iron red primer and a preparation method thereof. The primer comprises, by mass, 22.5-30% of a water-based acrylic emulsion, 3-10% of a waterborne epoxy ester resin, 0.25-0.5 % of a water-based dispersant, 0.2-0.4% of a water-based defoaming agent, 0.1-0.4% of a water-based base material wetting agent, 0.4-0.8% of an anti-flash rust agent, 5.3-10.1 % of deionized water, 3-6% of a film-forming additive, 0.2-0.4% of a drier, 0.3-0.5% of organic bentonite, 0.3-0.5% of fumed silica, 10-15% of iron oxide red, 27-32% of coarse whiting, 4-7% of water-based zinc phosphate, 3-5% of sericite, 3-4% of water-based aluminum phosphate and 0.2-0.4% of a water-based thickener. The product disclosed by the invention has the characteristics of good substrate oil stain resistance, good wetting adhesion on an oily repaired workpiece, and good wetting adhesion on a smooth curved surface, and a thick film formed by theproduct has the characteristics of no cracking, excellent impact bending resistance, good freeze-thaw resistance stability, good water resistance, excellent corrosion resistance, good heat resistanceand excellent adhesion; and the product can be widely applied to the fields of various large steel structures, automobile chassis paints, automobile water tanks, train chassis paints and engineering machines.