To further explore the failure mode and mechanical mechanism of reservoir-reactivated landslide, a new test device was designed and developed, the main body of which is composed of several permeable boxes, and it can simulate sliding surfaces with different geometric shapes. The sliding zone can be multi-stage softened by injecting water into different permeable boxes, so that the retrogressive-slide process between adjacent sliders caused by the rise of the reservoir water level can be realized. Through the techniques of digital photography, digital image processing, and transducers measurement, a series of important test data were obtained, such as volume water content, pore water pressure, horizontal displacement of slope, and evolution characteristics of the trailing edge surface. Moreover, the failure mode of the landslide body was discussed. Test results show that the significant decrease in shear strength of sliding zone soil after saturation was an important reason for the occurrence of landslide. The pore pressure variation at the sliding surface was the main inducing factor for the revival of the old landslide. The increase in pore water pressure at the sliding zone occurred simultaneously with the increase in the landslide displacement, and there was a good correlation between the strength degradation of sliding zone soil and the deformation of sliding body. The slope deformation area was divided into three parts: strong and weak deformation area and traction area. The slope deformation range was about 1 to 1.5 times the length of the unstable sliding zone. With the increase in the length of unstable sliding zone, the deformation zone of the slope increased, and the influence on the traction deformation of the back stable slope decreased. The trailing edge rupture surfaces were mostly in the shape of folded slip surface, and the experimental values of the inclination angle of the trailing edge surface were significantly affected by the position of the unstable sliding section and the thickness of the sliding body. The research results provide important basis for the understanding and controlling of landslide disasters in reservoir area.