CO₂ have long been recognized as indicators of deep Earth activity and are extensively used in the study of fault dynamics and tectonic movements. This article explores the chemical characteristics of deep-sourced CO₂,examining the three primary formation mechanisms—organic origin,metamorphic origin,and mantle origin—and methods for determining their sources. The study concludes that CO₂ in fault zones primarily originates from metamorphic and mantle sources. The paper reviews the progress of CO₂ observation in fault zones through three monitoring techniques:gas chromatography,CO₂ detector tubes,and digital CO₂ analyzers. It also outlines data processing and anomaly detection methods used in these studies. By analyzing earthquake case studies,the research demonstrates that CO₂ concentrations in fault zones can increase several times—often by a factor of ten or more—compared to background levels in the months or days preceding an earthquake. Finally,the study discusses the factors influencing CO₂ release from fault zones. CO₂ concentration is found to be positively correlated with underground stress intensity and temperature,while it is negatively correlated with atmospheric pressure and precipitation.