A copolyester and preparation method and use thereof are disclosed. In the diacid components constituting the copolyester, the content of the structure unit of terephthalic acid is 90 mol % or more. In the dihydric alcohol components constituting the copolyester, the content of the structure unit of ethylene glycol is 70-99 mol % and the content of the structure unit of aliphatic dihydric alcohol having 6 or less carbon atoms and having a side chain is 1-30 mol %. The copolyester further comprises a structure unit of polyethylene glycol. The copolyester can be made into fiber by common method, and further made into fabric, and the obtained finished-product has good dyeability to disperse dyes under normal temperature and normal pressure.