Collapsible loess is widely distributed in northwest China. Due to its large porosity and low strength, the construction of loess tunnel faces great difficulties and challenges. In order to investigate the effects of local water immersion in loess tunnel surrounding rock on tunnel structural stability, relying on the Jinping Tunnelin Dingxi, the tunnel model was established with the help of Midas/GTS. The comparison and analysis of normal excavation and local flooding were carried out respectively. The deformation rules and mechanical characteristics of surrounding rock and lining structure of loess tunnel after local flooding were studied. The results show that after normal excavation and water immersion, the maximum settlement value of surrounding rock appears in the tunnel arch, and the maximum settlement value after excavation is 9.60 mm, and the maximum settlement value increases to 13.18 mm after local water immersion. After normal excavation, the maximum principal stress of surrounding rock is 59 kPa. After water immersion, the maximum principal stress of surrounding rock appears at the arch and invert, and the maximum value is 89 kPa. The maximum compressive stress and the maximum tensile stress of the lining structure are 5.06 MPa and 2.08 MPa after the surrounding rock of the loess tunnel is partially flooded. The maximum compressive stress is 42% of the design strength, and the maximum tensile stress exceeds the design tensile strength.