Abstract: CO₂ is an important greenhouse gas that poses multifaceted hazards to the Earth's environment and human health. With the increase in industrialization, urbanization, and energy consumption, the emission of greenhouse gases such as CO₂ in the atmosphere has continued to increase, raising concerns about global climate change. Therefore, the detection of CO₂ concentration has become crucial. Currently, there are two main types of carbon emission measurement methods: testing methods and accounting methods. Testing methods have the advantages of high precision and real-time monitoring, making them more conducive to guiding the low-carbon transformation and operation of the unit compared to accounting methods. This paper mainly introduces the existing primary detection methods for CO₂, which include chemical analysis methods and physical optical analysis methods. Chemical analysis methods mainly include potentiometric titration, chemical absorption, gas-sensitive sensing technology, gas chromatography, and mass spectrometry. Physical optical analysis methods include cavity ring-down spectroscopy (CRDS), off-axis integrated cavity output spectroscopy (OA-ICOS), non-dispersive infrared (NDIR) absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and tunable diode laser absorption spectroscopy (TDLAS). Traditional chemical analysis is more suitable for accurate detection of complex components but is usually not suitable for long-period online detection. With the rapid development of computer technology and optical detection technology, emerging physical optical detection technologies gradually play a greater advantage. This paper summarizes and analyzes various detection methods that can help researchers select suitable CO₂ detection methods and provide data support for related industries. It can also help develop high-sensitivity and high-precision CO₂ metrology and detection equipment, which can aid in implementing the dual-carbon policy and controlling ambient air quality.