Jurassic landslides are widely developed in the Three Gorges Reservoir area. The study of the strength and deformation failure characteristics of the soft rock interlayer under different water pressures is of great theoretical significance to the long-term stability evaluation of the reservoir bank slope. MTS triaxial compression tests were carried out on the argillaceous siltstone of Shaximiao Formation, a typical soft rock of Jurassic in the Three Gorges Reservoir area, to study the strength and deformation damage characteristics of the rock under different water pressures. Based on fracture mechanics and effective stress principle, the mechanism of crack initiation and crack propagation under hydro-mechanical coupling effect was analyzed. It was found that water pressure can reduce the peak compressive strength of rock. With the increase of water pressure, the length and dip angle of dominant cracks increase, and the number of secondary cracks also shows a trend of increasing. The primary crack initiation and secondary crack propagation were controlled by KⅡ and KⅠ stress intensity factors, respectively. The maximum initiation angle of the primary crack was 70.5°. The critical propagation length of the secondary crack increases with the increase of the primary crack length. When the dip angle of the primary crack is about 45°, the propagation length of the secondary crack reaches the maximum under the same conditions. The results show that the existence of water pressure is conducive to the crack propagation, and the geometric characteristics of primary cracks also have a great influence on the crack propagation law.This study provides some theoretical guidance for the long-term stability evaluation of the reservoir bank rock mass.