The ongoing COVID-19 outbreak is the most serious public health crisis in the world in centuries. In its efforts for the epidemic, China has innovatively used the "health code"as a governing tool. The method has won applauses from many yet raised concerns and discussions from others. This paper reviews the basic concept, origins, contents, functions, use, technical framework, data sources, data management and data transmission of the health code for the pandemic control. It also reports popular evaluations of the effectiveness of the methods, its remaining issues and problems, rooms for improvements. Issues and problems discussed include precise identification and positioning risk groups, realization of efficient supervision of administrative rating and classification, reduction of discretional space, provision of discretional benchmarks, reduction of administrative execution burden, reduction of administrative costs, regional integration and collaboration, digital security, and privacy concerns. The authors then discuss the future implications and prospects of health code for intelligent health management and its potential to lead to other areas of smart city building.