Due to the instability of loess tunnel, studying their evolution under various conditions is essential for ensuring engineering construction. The comprehensive analysis about the mechanical properties of surrounding rock and failure mechanism of lining under different disaster-causing factors is needed. Based on the Baijiashan separated tunnel, 3 disaster-causing factors, surrounding rock grade, tunnel depth and bias condition are focused. A three-dimensional numerical model is established by finite difference method and above disaster-causing factors are considered. The displacement and stress evolutions of surrounding rock and lining are obtained. The plastic zone distribution of surrounding rock is discussed. The effects of 3 disaster-causing factors on surrounding rock and lining are analysed. The results indicate that the decrease of rock grade leads to an obvious increase in surrounding rock displacement and a significant decrease in tunnel stability. With the increasing tunnel buried depth, the maximum settlement displacement of the tunnel vault increases by 19 times, and the stress of the surrounding rock and lining keeps increasing linearly. Under bias condition, displacement and stress of surrounding rock and lining increase and no longer exhibit bilateral symmetry.