The underpassing of a large cross-section tunnel through a water conveyance tunnel may cause additional stress and deformation in the existing structure, potentially affecting the safety and stability of the water conveyance tunnel. Based on a large section tunnel project in the Heibaimian Jiangjun Hill, the blasting construction process under the tunnel is finely simulated by three-dimensional numerical simulation, the additional stress and deformation of the water conveyance tunnel are predicted, and the dynamic response characteristics are analyzed. The results show that the vibration of surrounding rock caused by static blasting construction of large-section tunnel mainly develops along the axial and vertical directions of water conveyance tunnel. The vibration speed and vertical stress increment of the water conveyance tunnel are concentrated within the intersection of the tunnel and the tunnel below. The static blasting method of tunnel underpass has relatively small disturbance to the water conveyance tunnel, which can ensure the safety and stability of the water transfer tunnel.