The invention discloses aqueous acrylic acid-modified alkyd resin and a preparation method thereof. Basic alkyd resin of the aqueous acrylic acid-modified alkyd resin is prepared from an unsaturated fatty acid, benzoic acid, trimethylolpropane, pentaerythritol, maleic anhydride, isophthalic acid, ethylene glycol monobutyl ether and butanol. The aqueous acrylic acid-modified alkyd resin is prepared by adding styrene, methyl methacrylate, butyl acrylate, acrylic acid, a silane coupling agent, benzoyl peroxide, tert-butyl hydroperoxide, ethylene glycol monobutyl ether and a mixing neutralizer into the basic alkyd resin. According to the aqueous acrylic acid-modified alkyd resin and the preparation method thereof, the advantages of alkyd resin and acrylic resin are integrated, and a product has high gloss retention, color retention and weather resistance; a production process is simple, the raw materials are readily available, and the production cost is low; a paint production process is simple, water is used as a diluting agent, and safety and convenience in construction are ensured.