The first formal comparison of gas flow primary standard facilities was conducted in China during 2016~2020. There were 4 participants from China, and PTB was invited as the link lab to connect this comparison with the serial key comparisons of CCM.FF.K5. There were 4 sets of sonic nozzles as the transfer meters, with which there were totally 105 set of measured results were conducted with the Reynolds range (4.8×10 4 ~1.1×10 7 ). To cover the Reynolds range, a theoretical equation of discharge coefficient was presented with only one parameter, which was used to evaluate the discharge coefficient at the exact same Reynolds number of the measured points. The evaluation model and uncertainty of the theoretical equation was presented. The degree of equivalence of En was finally evaluated. Among all 105 sets of measured results, there were 96 sets of results with En≤1; while there were 8 sets of results with 1