This article used the elastic-plastic finite element analysis method based on strength reduction theory and researched the regularity of longitudinal formation cracks during the loess tunnel construction. It analyzed the development trend of the crack dips and the distance between the surface crack and the tunnel center by different depth conditions when using the full section method and the bench cut method during the construction. From that it can get the boundary value of tunnel depth that the longitudinal crack can reach the ground. The result shows that: (1) Through the finite element analysis of the continuum structural model, it is feasible and effective to use the method, which is based on the area including the shear stress greater than the cohesive stress, the mutant horizontal displacement, and the change trend of the vertical displacement, to analyze the trend and the scope of longitudinal cracks after the excavation of the loess tunnels. (2) When using the full section method, the longitudinal cracks can reach the ground as long as the buried depth is less than 50m.With the increase of the buried depth, both of the depth of the cracks and the distance between the cracks and the tunnel center are all increased and the crack dips are changeable whose range is 56º~67º. However when the buried depth is more than 50m, the cracks can’t reach the ground and develop from the vault to the ground. The slip tendency near the ground is diminished. With the increase of the buried depth, the dips get larger, but the distance between the cracks and the tunnel center and the crack depth are invariable. (3) When using the-bench-cut method, the development trend of the formation crack is similar to that of the full section method. The cracks can reach the ground when the depth is less than 40m, and the range of the cracks is 56º~62º, or else the cracks can’t reach the ground. (4) From controlling the surface cracks, the bench cut method is superior to the full section method.