The cryogenic CO
2 removal technology can produce CO
2 as a high-purity liquid by-product while purifying NG, which has huge development prospects in the NG industry. Experimental and theoretical studies on the characteristics of CH
4-CO
2 binary mixtures and cryogenic CO
2 removal technologies in recent years have been classified and summarized in this paper. Compared to other CO
2 removal technologies, the cryogenic CO
2 separation has the following advantages. First, no chemical solvents are required, which will reduce the cost of frequently needed consumables and do not produce corrosion. In addition, this can also avoid the use of solvent recovery devices. In addition, no additional heating systems are required, which will reduce the heat consumption. Moreover, by-product liquid CO
2 can be used for EOR or other applications. Furthermore, if an integrated system is used and so is the cold energy from the regasification of LNG, the required cold energy can be obtained at a relatively low cost, and the system is highly economical. In Section 2, the characteristics of the CO
2-CH
4 binary mixture system are summarized experimentally and theoretically. Key parameters of experimental studies and models and methods of theoretical studies are listed in Tab.1 and Tab.2, respectively. From the summary, it can be seen that most of the experiments were performed within 110–220 K at 0–5 MPa, and the CO
2-CH
4 binary mixture phase behavior and frost point were studied by observation and using the sampling methods. The AAD of theoretical prediction is less than 10%, most of which are between 0.2%–3%, which is in good agreement with the experimental data. In Section 3, numerous researches for the cryogenic CO
2 removal technique in NG are presented and discussed. Different separation mechanisms, process structures, and working conditions lead to different separation effects and power consumption. The differences between those cryogenic CO
2 removal systems based on key parameters are listed in Tab.3 and Tab.4, respectively. It can be found that in the previous cryogenic CO
2 removal techniques, more researches are conducted on technologies based on gas-liquid phase change, while technologies that use gas-solid phase change are mostly applied in the field of flue gas purification. There are few applications of this technology in the field of NG, and the researches on cryogenic CO
2 removal technologies based on combined phase change are even more inadequate. In addition, the removal technologies based on gas-liquid phase change are mostly used for high CO
2 content feed gas, and the removal technologies based on gas-solid phase change are more suitable for the purification of feed gas with a lower CO
2 content. The purity of product CH
4 obtained by using the cryogenic CO
2 removal technology based on gas-liquid phase change is mostly higher than 95%, even up to 99.9%. At the same time, high-purity liquid CO
2 for EOR can be obtained by using this technology. Moreover, it can also be observed from Tab.3 and Tab.4 that the cryogenic CO
2 removal technology is mostly used for feed gas with a higher CO
2 content. The energy consumption of cryogenic CO
2 removal is lower than of the commercial chemical absorption method whose energy consumption is between 3.0 and 4.2 MJ/kg CO
2 [
87]. In response to this, Langè et al. [
88] also analyzed the economy of the traditional MDEA washing process and the low-temperature CO
2 removal process. The results show that when H
2S is not considered in NG and the CO
2 content is higher than about 8%–9% (mole fraction), the low-temperature technology has better economic efficiency.