Abstract: The theory of a dual-channel seepage model is proposed based on the phenomena and results obtained from the analysis of local seepage behavior in soil layers with a single fissure. By using the step function, the boundary conditions and transformation formula for rainfall-induced seepage are derived. Based on the existing rainfall infiltration models in literatures, the setting of the transition zone length for the step function is discussed. It is found that the calculated results are more accurate when the transition zone length is 4 or 8 units. Applying the above results, the dual-channel seepage effects are simulated using the COMSOL Multiphysics, and the deformation characteristics of the surrounding rock of tunnel with fractured soil under rainfall infiltration are explored. At the same time, a multi-factor impact analysis is conducted based on the factors that may affect the deformation characteristics of rainfall infiltration of the tunnel, including fissure location, rainfall intensity and fissure width. The results show that with the increase of rainfall time, the settlements of the arch and upper horizontal displacement of the tunnel at the side near the fissure are significantly higher than those at side the far from the fissure. The larger the fissure width, the faster the rainfall infiltration and expansion, and the greater the displacement generated by the tunnel. Comparing the settlement of the arch crown with a fissure width of 2 mm and the upper horizontal displacement, when there is a fissure width of 8 mm above the tunnel, the maximum settlement of the arch crown reaches 328 mm, an increase of 6.5%, and the maximum horizontal displacement of the upper part is 26 mm, an increase of 44%. The intensity of rainfall has a relatively small impact on the surrounding rock of the tunnel.