Objective To address the inconsistency of CNG national standards to other related standards at present, relatively scientific and reasonable quality indexes are proposed to promote the high-quality development of the CNG industry.

Methods Based on CNG quality status in China, domestic and foreign CNG standards, and CNG quality indexes, the determination of GB 18047 Compressed natural gas as vehicle fuel quality indexes and the optimization and revision in each stage were analyzed, and the international CNG quality indexes were compared.

Results With the rapid development of the national natural gas industry and the improvement of environmental protection requirements, the current CNG quality indexes could not reflect the clean attribute of natural gas, and the CNG quality level as a commodity was not classified, which was not conducive to the development of fair and equitable market trade.

Conclusions This paper proposes CNG quality indexes recommendations from the perspectives of safety, environmental protection, economic adaptability, and promoting industrial development, which are listed as follows: Firstly, CNG is classified into Class I and Class II based on its gross calorific value, total sulfur, H₂S content, and oxygen content. Secondly, gross calorific value of 34.0 MJ/m³, total sulfur content of 20 mg/m³, hydrogen sulfide content of 6 mg/m³, and the oxygen content of 0.1 vol% are added as technical indexes of Class I gas. Thirdly, indexes of GB 18047—2017 are kept for Class II gas to ensure the use of special gas sources to produce CNG. Fourthly, The water dew point index is modified to "in the specific geographical area of the car driving, under the conditions of operating pressure and ambient temperature below −13 ℃, there should be no liquid water precipitation in the compressed natural gas as vehicle fuel".