Abstract: Environmental self-purification is an inherent function of environmental systems for self-regulation and restoration. However， it has long remained a “popular yet vague” empirical concept， lacking a systematic theoretical framework and a clear pathway for engineering implementation. Based on a systematic investigation of environmental self-purification， this study advances the concept from "self-purification ratio" to "self-purification capacity" and defines it as the overall capacity of an environmental system to reduce or remove pollutants without causing ecological damage. At the theoretical level， we identify a fundamental issue in self-purification processes： pollutants may be removed while their ecological effects persist. Accordingly， we establish a kinetic formulation of self-purification capacity that integrates pollutant removal efficiency with ecological safety. At the methodological level， we develop a systematic framework for investigating self-purification capacity， encompassing evaluation indicators， data-mechanism fusion simulators， system restoration strategies， and intelligent regulation platforms. At the application level， we propose an engineering pathway that integrates physical， chemical， and biological driving forces by coupling natural purification with targeted human intervention. Our study demonstrates that restoring and enhancing the resilience of environmental self-purification capacity provides the scientific basis for a "pollutant discharge-self-purification balance" paradigm. This shift offers a core technological pathway for advancing environmental engineering from conventional end-of-pipe treatment toward ecologically intelligent governance.