The invention discloses waterborne polyester resin for industrial coatings prepared with a waste PET (polyethylene terephthalate) plastic bottle. The waterborne polyester resin is characterized in that a depolymerization monomer of the waste PET plastic bottle is taken as a main raw material for a reaction; the depolymerization monomer is firstly subjected to an esterification copolymerization reaction with polyols and polyacids, then reacted with fourth reactive monomers such as an organic silicon monomer, an organic fluorine monomer, an acrylic acid monomer, an epoxy monomer, an isocyanate and the like for chemical modification, and then reacted with a waterborne monomer for end-capping modification; and finally a diluent is used for diluting to form the waterborne polyester resin. According to the invention, the depolymerization monomer of the waste PET plastic bottle is directly used as one of the raw materials for preparing the waterborne polyester resin for the industrial coatings, a considerable portion of the polyols and the polyacids is replaced to prepare the waterborne polyester resin for the industrial coatings, so that the problem that the high cost caused by the extensive use of a large amount of the expensive polyols and the polyacids in the prior art is overcome on the premise of ensuring the excellent quality and performance of products, and the problems of high cost and low efficiency in recycling and reusing of waste PET plastic bottles are indirectly solved.