At present, the epidemic of Coronavirus Disease 2019 (COVID-19) is spreading worldwidely. Humans may be compelled to live with the viruses for a long time. The asymptomatic infections are contagious and the most difficult to control, easy to cause the accumulation of infection sources in the community. More and more asymptomatic cases have brought great challenges to the control of the epidemic. This review provides relatively comprehensive and updated information about asymptomatic cases of COVID-19. We find most of asymptomatic carriers are young people, and there are more asymptomatic infections in children compared with adult patients. Some asymptomatic carriers especially children have a longer communicable period than the confirmed cases. There is a risk of reoccurrence of positive result of nucleic acid test in asymptomatic cases. The chest CT findings of asymptomatic infections were mainly GGO , mostly peripheral distribution and restored quickly. Aerosol and fomite transmission of SARS-CoV-2 by asymptomatic carriers is plausible, so every person releases potentially infectious aerosols all the time. All countries in the world should raise public awareness of protection and strengthen social security measures to prevent second outbreak caused by the asymptomatic infections.