In addition to the structural genes of the coronavirus genome, S, E, M, and N, there are several additional genes called "group-specific or accessory genes". Their gene products are designated as "accessory proteins", as reports to date make it clear that these proteins are not essential for virus replication in vitro. Nevertheless, many of these genes are still maintained in the virus genome under selective pressure, suggesting that they might play a very important role in the survival of the virus in the natural environment of the infected host. This review will summarize the research progress in the functions of coronavirus accessory genes.