Reverse top-lifting construction method for tunnel with large abrupt change cross section

The invention relates to the technical field of underground tunnel construction, and particularly discloses a reverse top-lifting construction method for a tunnel with a large abrupt change cross section, top-lifting construction is performed by adopting a temporary support arch frame, reverse top-lifting construction is performed after an upper step of a main cavern is communicated, and the reverse top-lifting construction method comprises the following steps: S1, surveying and setting out; s2, excavating and supporting a variable cross-section section; s3, excavating and supporting a main cavern; s4, reversely picking a primary support; s5, inverted arch and filling construction; and S6, secondary lining and end wall construction. The method can be suitable for the situation that the small section and the large section in the abrupt change section are greatly different, the operation space is large, the construction efficiency is high, in addition, partial supports of the pilot tunnel can be completely recy