Research conclusions:From the analysis of the load bearing and deformation of key parts of the tunnel structure system during the excavation，it is concluded: (1) During excavation，the stress and deformation of the key positions of the left and right caverns and on the top of the middle partition wall follow the change regulation of the construction process．(2) The three bench of the middle pilot tunnel + right pilot tunnel + left tunnel is available for construction of such kind tunnel．(3) The unbalance support system should be used for the large span unsymmetrical multi － arch tunnel．(4) In order to solve the problem of water leakage on the top of the middle partition wall，the small pilot pipe should be installed and grouting should be conducted in the V area on its top． The rock on the top of the middle partition wall should be reinforced to improve its impermeability． The calculation result provides the reliable basis for the tunnel design and the reference to the similar works．