Abstract: C-ring is the core part for seal of the reactor pressure vessel top cover and cylinder, and the sealing performance is directly related to the safety and stably operation of the nuclear power plant. For a long time, the manufacturing technology of C-ring was monopolized by foreign company, with high price and long supply cycle. It is verified that the C-ring made in China fulfill the commercial application, through sealing properties test, helium leak detection test, water pressure test and thermal-cold cycle test. The functional impact analysis proved the equivalence of the domesticated C-ring. The installation quality of domestic C-ring was strictly controlled in nuclear power plant, and the performance of the domestic C-ring was verified by the in-service hydraulic test and the running test.