A titanium catalyst and a synthesizing method of polyester resins are provided in the present disclosure. The titanium catalyst has a chemical structure represented by Formula (I), Formula (II) or Formula (III).




The symbols shown in the Formula (I), the Formula (II) or the Formula (III) are defined in the description. The synthesizing method of polyester resins includes providing the titanium catalyst, performing a feeding step, performing a heating and pressurizing step and performing a heating and vacuuming step. The titanium catalyst and a heat stabilizer are added into an autoclave before the feeding step or before the heating and vacuuming step.