The "black code" of the electronic health code indicates that the epidemiological questionnaire has expired and needs to be filled in again. Green means you can enter normally and pass within the range. As an individual entering and leaving electronic certificate locally, the QR code can be declared once, which is universal in the whole city. The introduction of the health code aims to make the work of returning to work more accurate, scientific and orderly. The green code can pass normally, but the black code can't pass normally.