Abstract： By April 28, 2020, the global pandemic of COVID-19 has resulted in over 3 million infections and more than 200, 000 deaths. As the epidemic of COVID-19 has been basically controlled in China, the asymptomatic infection becomes one of most serious challenges for "External defense input, internal defense rebound" currently. Studies have shown that patients with asymptomatic infections are highly contagious in the early stage, most of whom are in the pre-symptomatic stage. Children and pregnant women have a higher incidence of asymptomatic infections, but the impacts are not yet clear. This article reviews the definition, epidemiological characteristics, contagiousness, viral shedding and cause of persistent positive nucleic acid in asymptomatic patients. Active detection of nucleic acids and antibodies and timely diagnosis and treatment of asymptomatic cases are the critical issues for the prevention and control of COVID-19.