Abstract: This study systematically investigates the swelling behavior and mechanism of perfluoroether rubber (FFKM) in anhydrous and aqueous methanol environments. Using SEM, FT-IR, and mechanical performance testing methods, comparative analyses were conducted on FFKM after 7 days of immersion in different methanol media, focusing on changes in volume, surface and fracture morphology, mechanical properties, and functional group structures. Experimental results indicate that FFKM exhibits more pronounced swelling and performance degradation in anhydrous methanol, manifested by significant increases in volume and mass, damage to surface and fracture structures, and reductions in hardness and mechanical strength. In contrast, methanol solution containing 8 wt% water shows a certain inhibitory effect on the swelling behavior. Combining infrared spectral analysis at the molecular level with discussion of the swelling mechanism, the study reveals the complete process through which methanol molecules affect the microstructure and macroscopic properties of FFKM via diffusion, hydrogen bonding, and polymer chain relaxation. This research provides a theoretical basis for the selection and modification of sealing materials used in methanol pipelines.