Abstract: Hu Hongji, as the director of metropolitan medical services, was the first person to apply modern public health theory to the construction of urban public health in China. He also introduced a complete concept of public health and gave a high-level generalization of its nature, content, purpose and methods for the first time. His public health thought is reflected in the following: Prevention of infectious diseases is the policy of health administration; Prevention of infectious diseases among the poor in shantytowns is the focus of health administration; Perfect vital statistics is a prerequisite for the development of public health; Socialization of medicine is the way to solve the problem of high mortality rate among the poor; The strength of the nation depends on whether families and schools pay attention to children's health; Children's health is the responsibility of both families and schools; Rural sanitation is no less important than urban one. The formation of this thought is closely related to his professional background in public health, his life experience and the national conditions of modern China.