The health code turns yellow for the following reasons: 1. The confirmed cases in COVID-19 were found in the area where they were located, and were divided into control areas, and the health codes of the people in the control areas were given yellow codes. 2. The health code of those suspected to be consistent with the confirmed cases in COVID-19 is updated to yellow code. For example, the health codes of sub-secret contacts and time-space contacts will be assigned yellow codes. 3. I went to the middle and high risk areas of the epidemic, such as the regional investigators of the epidemic, and the health codes of the personnel in the middle risk areas in the past 14 days were given yellow codes. 4. A comprehensive nucleic acid test is needed, but without nucleic acid test, the health code will be given a yellow code. 5. The person whose personal mobile phone number and identity information match the yellow code. 6. Self-reported health information appeared: people with fever, shortness of breath and respiratory symptoms. 7. Persons within 14 days after confirmed cases are cured, persons within 14 days after asymptomatic infected persons are released from isolation, and persons within 14 days after suspected cases are excluded.