The aging behavior of carboxy nitroso fluororubber in a liquid dinitrogen tetroxide （N₂O₄） medium was investigated using several analytical techniques. The results indicated that the glass transition temperature （T_g） of the samples did not change significantly with the increase of aging days， but the thermal stability of the samples decreased and swelling ratio increased. Meanwhile， microcracks gradually appeared on the surface of the samples. These results indicate the samples gradually aged in the liquid medium. X-ray photoelectron spectroscopy （XPS） results revealed that compared to the unaged samples， the proportion of elements on the surface of the aged samples did not change significantly，but some crosslinking points were destroyed. The thermogravimetric analysis-Fourier transform infrared spectroscopy-gas chromatography/mass spectrometry （TGA-IR-GC/MS） result showed that the surface modifier of silica filler undergo oxidation in N₂O₄ medium during the aging process， thus reducing the thermal stability of the samples.