This paper reviews existing gas sensing technologies, classifying them based on variations in electrical and other properties. It discusses various sensing methods, including those based on metal oxide semiconductors, polymers, carbon nanotubes, and moisture-absorbing materials, as well as optical, calorimetric, acoustic, and gas-chromatographic methods. The paper highlights two key performance indicators: sensitivity (the minimum detectable gas concentration) and selectivity (the ability to distinguish target gases from others). It analyzes factors influencing these indicators and presents improved approaches to enhance them. The review also discusses the application of gas sensors in various fields, such as industrial production, automotive industry, medical applications, indoor air quality monitoring, and environmental studies. The paper emphasizes the importance of sensitivity and selectivity in gas sensing and provides suggestions for future research directions. It concludes that while metal oxide semiconductor-based sensors are widely used, their high operating temperatures and sensitivity issues limit their applications. Alternative materials like carbon nanotubes and polymers offer advantages in terms of sensitivity, selectivity, and operating temperature. The paper also discusses the challenges of gas sensor stability, including design errors, structural changes, phase shifts, poisoning, and environmental variations. It suggests methods to improve sensor stability, such as using chemically and thermally stable materials, optimizing sensing material composition, and utilizing surface pretreatment technologies. The paper concludes that research on gas sensing technologies should focus on overcoming the inherent limitations of existing sensors to improve their performance and expand their applications.This paper reviews existing gas sensing technologies, classifying them based on variations in electrical and other properties. It discusses various sensing methods, including those based on metal oxide semiconductors, polymers, carbon nanotubes, and moisture-absorbing materials, as well as optical, calorimetric, acoustic, and gas-chromatographic methods. The paper highlights two key performance indicators: sensitivity (the minimum detectable gas concentration) and selectivity (the ability to distinguish target gases from others). It analyzes factors influencing these indicators and presents improved approaches to enhance them. The review also discusses the application of gas sensors in various fields, such as industrial production, automotive industry, medical applications, indoor air quality monitoring, and environmental studies. The paper emphasizes the importance of sensitivity and selectivity in gas sensing and provides suggestions for future research directions. It concludes that while metal oxide semiconductor-based sensors are widely used, their high operating temperatures and sensitivity issues limit their applications. Alternative materials like carbon nanotubes and polymers offer advantages in terms of sensitivity, selectivity, and operating temperature. The paper also discusses the challenges of gas sensor stability, including design errors, structural changes, phase shifts, poisoning, and environmental variations. It suggests methods to improve sensor stability, such as using chemically and thermally stable materials, optimizing sensing material composition, and utilizing surface pretreatment technologies. The paper concludes that research on gas sensing technologies should focus on overcoming the inherent limitations of existing sensors to improve their performance and expand their applications.