The invention relates to a civil engineering traffic construction industry foundation pit project, in particular to an enclosure structure of the foundation pit which is used under the foundation pit and carries out the shield structure zone tunnel crossing construction; the enclosure structure with the ultrashort underground wall comprises underground walls, steel supports, reinforced concrete supports and reinforced concrete enclosing purlins which are arranged among the underground walls, and is characterized in that the underground wall of the foundation pit in the crossing section range of the shield structure is the ultrashort underground wall, the wall toe of which is arranged under the top of the shield structure by no less than 0.5m; the short wall support of the underground wall embedded under the bottom of the foundation pit is transversely arranged between every pair of ultrashort underground walls at both sides of the foundation pit; the wall toe of the short wall support of the underground wall is flush with the wall toe of the ultrashort underground wall; the enclosure structure has the advantages that the enclosure structure can ensure the smooth crossing of the later stage shield structure, and compared with the traditional shield structure which passes through the glass fiber reinforced plastic underground wall, the enclosure structure reduces the risk and construction cost of the project.