Abstract: To get lightweight, highly hygroscopic materials, Schiff base composite coating was prepared to hydrophilically modify the matrix material to improve the hygroscopic performance. Glutaraldehyde (GA) as an intermediate was used to covalently link aminated nano-silica (SiO₂) and the hydrophilic substance 2-(2-aminoethyl)amino ethanesulfonate sodium (AAS) to prepare Schiff base composite material (SiO₂-NH₂-GA-AAS), and then the SiO₂-NH₂-GA-AAS / CS composite coating was prepared by dispersing it in chitosan (CS) solution. The polymer polyethylene terephthalate alcohol (PET) was used as the base material, and the composite coating was coated on its surface by dipping to modify it. FTIR, field emission scanning electron microscope equipped with energy dispersive spectrometer (FESEM-EDS) and contact angle measuring instrument were used to test the microscopic morphology, element distribution and surface wettability of the PET substrate coated with composite coating. The adsorption process was fitted with Pseudo-first-order and Pseudo-second-order kinetic models. The results show the modified PET substrate has the best hygroscopic performance when mass ratio of SiO₂-NH₂/AAS is 1∶2 and the amount of SiO₂-NH₂-GA-AAS is 10wt%. From the FESEM-EDS analysis, it can be seen that the surface of the modified PET substrate is coated with a uniform composite material, and the contact angle changes from the original 135° to 0°, achieving the super-hydrophilic effect. In the environment of 25℃, 97% relative humidity (RH), the PET substrate coated with the optimum composite coating reaches moisture saturation after 45 h of moisture absorption which reaches 36.94% moisture content. The moisture absorption performance has been extremely improved. The whole adsorption process conforms to the Pseudo-second-order kinetic model.