Although single-atom Cu sites exhibit high efficiency in CO hydrogenation to methanol, they are prone to forming Cu nanoparticles due to reduction and aggregation under reaction conditions, especially at high temperatures. Herein, single-atom Cu sites stabilized by adjacent Na ions have been successfully constructed within a metal-organic framework (MOF)-based catalyst, namely MOF-808-NaCu. It is found that the electrostatic interaction between the Na and H species plays a pivotal role in upholding the atomic dispersion of Cu in MOF-808-NaCu during CO hydrogenation, even at temperatures of up to 275°C. This exceptional stabilization effect endows the catalyst with excellent activity (306 g·kg·h), high selectivity to methanol (93%) and long-term stability at elevated reaction temperatures, far surpassing the counterpart in the absence of Na (denoted as MOF-808-Cu). This work develops an effective strategy for the fabrication of stable single-atom sites for advanced catalysis by creating an alkali-decorated microenvironment in close proximity.