How to design form of public health facilities effectively is the key to enhance the city's image and create urban civilization. But now there are many deficiencies in form design of public health facilities in our country. In this paper, the design method of public health facilities is discussed with the design case of new city mobile public toilet. Confirm the design idea which is based on the modular theory and taken into account many factors can solve the form problem of city mobile public toilet. So as to provide reference for the public health facilities design.