The invention discloses a combined steel temporary supporting excavation method for a tunnel with an extra-large section. The combined steel temporary supporting excavation method comprises the following steps of: firstly excavating and supporting left and right upper pilot tunnels; secondly excavating and supporting left and right middle pilot tunnels, and left and right lower pilot tunnels, and excavating a pilot tunnel on the left lower part of the tunnel section; thirdly, setting temporary mid-partition supports and temporary steel supports for all parts; and finally, dismounting the temporary combined upright post steel supports of the left upper pilot tunnel and the right upper pilot tunnel, and pouring the second liner reinforced concrete, excavating core soil and carrying out inverted arch construction to the middle part of the tunnel. The combined steel temporary supporting excavation method uses a combined steel support to replace a temporary excavation method of the core soil, solves the technical difficulties that the excavation period is long, the construction quality cannot be ensured, the construction is difficult, and the like, and also solves the technical problems of ensuring the quick construction for the super-large section and the construction quality. A steel truss is used to replace the construction for the upper core soil, so that not only the construction safety of the tunnel can be improved, but also the tunnel excavation and the support speed can be quickened.