The change of water content in the basement rock of loess tunnel will lead to the instability and even collapse of arch foot and wall foot. Therefore, the research on the mechanical properties of loess tunnel, especially the tunnel in collapsible loess stratum as a whole, has attracted great attention of engineers and technicians. In order to study the bearing capacity and collapsible deformation of tunnel base in collapsible loess stratum, the stress and deformation characteristics of natural base under water immersion and non water immersion conditions are studied through indoor large-scale model test. The results show that the radial distribution of tunnel base pressure is non-uniform, which is the smallest in the middle of inverted arch and the largest at the foot of wall; The variation law of tangential stress around the tunnel is basically similar to that of radial stress, but the variation range is small; The tangential pressure and radial pressure of the tunnel are basically the same, and the stress values of each measuring point increase after immersion.