Regulating the coordination environment via heteroatoms to break the symmetrical electronic structure of M-N-4 active sites provides a promising route to engineer metal-nitrogen-carbon catalysts for electrochemical CO2 reduction reaction. However, it remains challenging to realize a site-specific introduction of heteroatoms at atomic level due to their energetically unstable nature. Here, this paper reports a facile route via using an oxygen- and nitrogen-rich metal-organic framework (MOF) (IRMOF-3) as the precursor to construct the Fe-O and Fe-N chelation, simultaneously, resulting in an atomically dispersed axial O-coordinated FeN4 active site. Compared to the FeN4 active sites without O coordination, the formed FeN4-O sites exhibit much better catalytic performance toward CO, reaching a maximum FECO of 95% at -0.50 V versus reversible hydrogen electrode. To the best of the authors' knowledge, such performance exceeds that of the existing Fe-N-C-based catalysts derived from sole N-rich MOFs. Density functional theory calculations indicate that the axial O-coordination regulates the binding energy of intermediates in the reaction pathways, resulting in a smoother desorption of CO and increased energy for the competitive hydrogen production.