Negative nucleic acid for novel coronavirus means no infection with novel coronavirus, as for 7d generally means 7 days. The nucleic acid test of new coronavirus is mainly qualitative at present, including negative and positive, weak positive. Among them, negative means there is no infection of the new coronavirus and it is a normal population, while positive and weak positive represent infection of the new coronavirus. If the test is still negative after 7 days of close contact, the infection cannot be ruled out completely because the incubation period of New Crown Virus may be two weeks or even longer, so the nucleic acid of New Crown Virus still needs to be monitored in the following time. Nucleic acid testing for neocoronaviruses is by far the most important means of screening and has a relatively high accuracy rate. Anyone at risk should be screened regularly.