The invention discloses a PIA (meta-phthalic acid) / nanometer titania modified alkyd resin and a preparation method thereof. The PIA / nanometer titania modified alkyd resin comprises the following raw materials: acrylic acid, methylacrylic acid, methyl methacrylate, vinyltriethoxysilane, nanometer titania, epoxy resin, castor oil, trimethylolpropane, 2,2,4-trimethyl-1,3-pentanediol, tetrachlorophthalic anhydride, PIA waste, trimellitic anhydride, triethylamine, ethyl eneglycol monobutyl ether, propylene glycol mono-n-butyl ether, lauric acid, catalytic auxiliary, benzoyl peroxide, dimethylbenzene and water. The PIA / nanometer titania modified alkyd resin provided by the invention is good in water resistance, high in hardness and excellent in comprehensive performance; the PIA waste is used, so that the cost is saved.