A preparation method of a polyester resin includes: under predetermined depolymerization conditions, mixing a polyester resin, a resin dissolvent and a polycondensation catalyst to depolymerize the polyester resin and form a first reaction mixture; adding a first monomer to the first reaction mixture to form a second reaction mixture; under predetermined polymerization conditions, adding a second monomer to the second reaction mixture to polymerize the depolymerized polyester resin and form a third reaction mixture; and adding a neutralizing agent to neutralize the polymerized reaction product of the third reaction mixture.