The invention discloses an organic amine ended low-side carboxyl group content polyester which is prepared by adopting the following raw materials by weight part: 10000-18000 parts of dibasic acid monomer, 1800-6500 parts of glycol, 1-10 parts of catalyst, 2-10 parts of stabilizer, 2-50 parts of opening agents and 1.3-7.5 parts of organic amines. A polyester film provided by the invention has excellent tone, high separating performance, high thermal stability, excellent damp-heat aging resistance, long service life, higher tensile strength, high size stability and wide application in the fields of construction substrates, solar cell backboards, and the like.