The function of health code is to quickly identify whether a person has directly or indirectly contacted infected patients through the color of health code. Then through big data analysis, you can directly lock and find people who may be infected. The "health code" is based on real data and can be generated by citizens or people who have returned to work through their own online declaration and background audit. As a personal entry and exit area in electronic certificate, the QR code can be declared once, which is universal in the whole city.