The present invention discloses a multi-granularity and multi-level expression method of urban rail transit composition structure, and relates to the technical field of model expression of urban rail transit design. (1) establishing an abstract data model of urban rail transit engineering consisting of seven dimensions such as specialties, components, three-dimensional geometry, cost, time period, etc.; (2) bipartite canonical coding of the composition of the entire urban rail transit engineering and forming a coding structure tree; (3) mapping the seven-dimensional data model to the coding structure tree to form a canonically organized data sequence; and (4) establishing IFC based on the built-in coding logic and the IFC-based entity + relational data expression of attributes, to establish a computer-accessible expression based on coded IFC objects + attribute data that can be extended to the full life cycle. By decomposing the complex urban rail transit system engineering body into the smallest granularity expression and combining it with a codable structural tree, it is mapped into an integrated data model with object-oriented and relational data expression in the computer.