In this paper,the interaction between water molecules and PETG copolymers was investigated by low-field nuclear magnetic resonance(LF-NMR)and Fourier transform infrared spectroscopy Attenuated total reflection-Fourier transform infrared spectroscopy(ATR-FTIR).The water state and distribution of Poly(ethylene terephthalate)-Poly(ethylene glycol)(PETG)copolymer during water adsorption were analyzed.A model of the interaction between water and PETG copolymers was proposed that there are three categories of water in PETG copolymers during water adsorption process.It is believed the method developed could be also applied to investigate various interactions between macromolecules and other small molecules without using deuterium samples.