The invention relates to a method for preparing a terephthalic acid glycol 1,2-propanediol copolyester. The method comprises the following steps of: compounding a titanium compound, an antimony compound, a cobalt compound and a phosphorus compound into a catalyst; reacting pure terephthalic acid or dimethyl terephthalate with glycol and 1,2-propanediol in the molar ratio of 1:1.0-2.2; performing esterification or transesterification under the pressure of 0.25MPa or normal pressure and at the temperature of 170 to 250 DEG C to obtain terephthalic acid 1,2-propanediol terephthalate, ethylene glycol terephthalate and oligomers of the terephthalic acid 1,2-propanediol terephthalate and the ethylene glycol terephthalate, wherein the molar ratio of glycol to 1,2-propanediol is 5:95-90:10; and reducing the pressure of an reaction kettle to 10 to 150Pa to distill byproducts micromolecular dibasic alcohol and the oligomers out and obtain a polymer melt at the final reaction temperature of 265 to 280 DEG C, wherein the copolyester has a tensile modulus of 1,450 to 1,550MPa, a bending strength of 85 to 95 MPa and a bending modulus of 2,650 to 2,800MPa.