Atomic oxygen (AO) collision is one of the most serious threats to polymeric materials exposed to the space environment, yet understanding the structural changes and degradation of materials caused by AO impact remains a tremendous issue. Herein, we systematically evaluate the erosion collision and mechanical degradation of polyether ether ketone (PEEK) resin under hypervelocity AO impact using reactive molecular dynamics simulations. The interaction process and local evolution mechanism between high-speed AO and PEEK are investigated for the first time, suggesting that AO will either be scattered or adsorbed by PEEK, which is strongly correlated with the main degraded species evolution including O2, OH, CO, and CO2. Different AO fluxes and AO incidence angle simulations indicate that high-energy AO collision on the surface transfers kinetic energy to PEEK's thermal energy, thus inducing mass loss and surface penetration mechanisms. Vertically impacted AO causes less erosion on the PEEK matrix, rather than obliquely. Furthermore, PEEK chains modified with functional side groups are comprehensively investigated by 200 AO impact and high strain rate (1010 s-1) tensile simulations, demonstrating that the spatial configuration and stable benzene functionality of phenyl side groups can significantly improve the AO resistance and mechanical properties of PEEK at 300 and 800 K. This work revealed useful insights into the interaction mechanisms between AO and PEEK at the atomic scale and may provide a protocol for screening and designing new polymers of high AO tolerance.