Abstract: The Wangjiadun landslide in Qinan County, Tianshui City is a huge ancient landslide group along the Baoji-Lanzhou High-speed Railway, with the Qinan tunnel passing through it. By taking Wangjiadun ancient landslide as the studying object and centering on its static and dynamic anti-sliding stability, the intrinsic factors, such as geological structure and site engineering conditions, has been analyzed and evaluated in this paper, which affect the stability of Wangjiadun ancient landslide through indoor and field test. And then, the dynamic response of Wangjiadun ancient landslide under earthquake load has been analyzed by finite element dynamic analysis method, and the relationships between the stability factors influencing, earthquake load and landslide instability & failure under earthquake load for the Wangjiadun ancient landslide have been defined. In addition, the study on dynamic anti-sliding stability analysis has been carried out by using the dynamic finite element method combined with strength reduction method. The results show that the horizontal thrust under earthquake action has a great influence on the stability of Wangjiadun ancient landslide, which is manifested as the overall slip of upper slope and the local instability collapse of loess accumulative formation at the tunnel. Therefore, the method of displacement catastrophe can be used to determine the dynamic instability and dynamic safety factor of the slope.It is manifested as the overall slip of upper slope and the local instability adn collapse of loess accumulative formation at the tunnel. Therefore, the method of displacement catastrophe is used to determine the dynamic instability and dynamic safety factor of the slope.