Abstract: Based on the Tangjiayuan highway tunnel on the Xi′an-Baoji expressway, the influential factors regarding magnitude and direction of a landslide's thrust acting on the lining of an arched tunnel with a straight wall are analyzed in light of the positional relationship between the tunnel and the sliding surface. A theoretical calculation method for the internal force distribution of a semicircle arched tunnel lining is obtained, with the sliding direction being orthogonal to the axis. Using the Tangjiayuan tunnel as an example, the internal force distribution of a tunnel lining is obtained by theoretical calculation, and the rationality and validity are verified by FEM, with the results showing that this method can be used to calculate the internal force of a tunnel lining in the case of the landslide sliding direction being orthogonal to the tunnel axis.