Abstract: During the outbreak of COVID-19, early quarantine from high risk areas is an effective measure to curb the spread of the epidemic. To avoid people leaving the quarantine area without authorization, a large number of supervisors are required to conduct 24 hours supervision, which not only needs much of labor and money, but also have the problems of information leakage, non real-time information collection and the safety of supervisors. It is necessary to realize automatic real-time quarantine monitoring by using the existing infrastructure. This paper realized it by collecting and analyzing the position and carrier noise ratio (CNR) information of Global Navigation Satellite System (GNSS) chip receiver in cellphone. Through analysis of the actual detection data, the result shows that the method can accurately and effectively distinguish whether the people leave of the quarantine area.