Nucleocapsid, nucleocapsid protein, is an important structural protein of novel coronavirus SARS-CoV-2, which is responsible for wrapping the virus RNA genome to form a long spiral nucleocapsid complex (Long Helical Ribonucleocapsid complex, RNP), and then assemble into virus particles. Nucleocapsid can induce host immune response. Among the infected cells, the abundance of Nucleocapsid is the highest and the detection is the most convenient. In SARS-CoV-2 mutants, Nucleocapsid is highly conserved. The antigen detection kit developed for this protein can effectively avoid mutation escape and improve the detection accuracy. The high abundance and high conservation of Nucleocapsid make it the most ideal antigen for the development of SARS-CoV-2 antigen detection kit and play an important role in SARS-CoV-2 detection.