Abstract: In this paper, the Jianchuandong dangerous rock mass in the Three Gorges Reservoir area is taken as an example to study the failure mode and protection of submerged thick-layer dangerous rock mass. Based on field investigation and the monitoring data, it was found that the degradation of the base rock mass under the dry-wet cycles is the main factor to accelerate the deformation of the dangerous rock mass. Its failure mode is determined as slip collapse. According to the deformation and failure characteristics of the dangerous rock mass, the corresponding treatment measure is divided into two parts, inculding the reinforcement of the weak base rock mass, and anchor cable in the upper part of the dangerous rock mass. By comparing the displacement field and the stress field before and after protection, it is found that the prestressed reinforcement of the upper dangerous rock mass can effectively control the deformation of the rock mass, and the reinforcement of base rock mass can effectively control the maximum shear stress of the dangerous rock mass. The comprehensive protection effect is significant to ensure the stability of dangerous rock mass. The protection method can provide important reference for the treatment of submerged dangerous rock mass in the reservoir area.