Abstract: The creep rock mass zone B is located in the upstream of Long-Tan hydropower station.It is the typically toppling rock slope.Because of weathering,unloading and other external stress,the slope has occurred fracture and slide deformation.Then the slope stability was paid much attention by engineers.The purpose of this paper is to investigate the structural feature of the reservoir area,and to analyse the slope stability from rock mass,and then to offer the scientific evidences for slope stability in qualitative or quantitative analysis.The paper also discusses the assessment methods about rock mass quality,and proposes the concept for dynamic evaluation of rock mass quality.