Pre-assembled underground structure based on drop shaft sinking and construction method

The invention is applicable to the technical field of underground engineering, and provides a pre-assembled underground structure based on drop shaft sinking. The pre-assembled underground structure comprises bit angles, a side wall, a middle column, brackets, an annular stiffening beam, a prefabricated plate, a cast-in-place plate and a longitudinal beam, wherein the prefabricated part is formedby factory prefabrication of standard components and is mounted in a foundation pit after caisson drop shaft structure is formed after ground assembly is finished. The cast-in-place part adopts a cast-in-place manner, the problems that a traditional mode is low in efficiency and engineering quality is difficult to guarantee, are solved, the end heads of prefabricated slabs are connected with the annular reinforcing beam or a longitudinal beam, connectors are subjected to cast-in-place and solidified, foundation pit excavation is achieved through sinking of the drop shaft structure, and the side wall is supported throu