The utility model discloses a supporting system for large cross section tunnel construction in a soft geological environment so as to solve the problem of process interference caused by partial excavation through a traditional construction method and built a larger cross section tunnel safely and quickly under an extremely soft environment. The supporting system comprises a full-circular primary support structure, a full-circular secondary lining structure and a cross temporary support system, wherein the full-circular primary support structure is composed of a left upper pilot tunnel primary support, a right upper pilot tunnel primary support, a left lower pilot tunnel primary support and a right lower pilot tunnel primary support through the stepped excavation and construction of a left upper pilot tunnel, a right upper pilot tunnel, a left lower pilot tunnel and a right lower pilot tunnel; the full-circular secondary lining structure comprises a left upper pilot tunnel secondary liner, a right upper pilot tunnel secondary liner, a left lower pilot tunnel secondary liner and a right lower pilot tunnel secondary liner; the cross temporary support system comprises an upper partition vertical brace, a lower partition vertical brace, a left partition transverse brace and a right partition transverse brace; the outer end of the cross temporary support system is fixedly connected with the full-circular primary support structure and the full-circular secondary lining structure.