The work aims to specify the effect of modified nanocrystalline cellulose (NCC) on improving the thermal aging resistance of composite binder, with NCC modified by 3-glycidoxypropyltrimethoxysilane (MPS) and then added to waterborne polyurethane (WPU) for the preparation of the composite binder. The appearance morphology and chemical structure of composite binder were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectrophotometer (FT-IR). The thermally induced weight loss, specular gloss and peel strength of composite binder after processing under different aging conditions were determined. Compared to the original binder subject to aging treatment under the same conditions, when the composite binder containing 2.0% modified NCC was subject to aging treatment at 140 ℃ for 96 h, its weight loss rate was reduced by 5.9%. After a 96 h aging treatment at 140 ℃, the specular gloss and peel strength of the composite binder containing 2.0% modified NCC were respectively reduced by 51.1% and 44.7%, which were obviously less than those of the original binder under the same conditions. The addition of modified NCC can significantly improve the thermally induced weight loss of the binder and effectively reduce the damages of high-temperature treatment caused to coating specular gloss and peel strength.