In order to further improve the design theory of urban underground utility tunnel and help to design more scientifically and rationally, the concept of "section" is summarized and applied to the overall design of utility tunnel after large number of engineering practice. Based on the analysis of the functional requirements of utility tunnel and the technical requirements of access pipelines, various "functional sections" in utility tunnel are defined and characterized. And then, through comprehensive analysis of the interrelation and importance of various functional sections, the replicable "unit section" with compound functional attributes are constructed based on functional sections. Meanwhile, through duplication and series connection of unit sections, system layout of general design of the utility tunnel can be conveniently built up. Finally, by taking the "unit section" as the core concept, the definition and general method of "sectional design" of utility tunnel are proposed, which provides a new design method for the overall layout of utility tunnel′s engineering system.