Abstract:There are many engineering geological problems about hydroelectric development in west of China,which will lead to a large effect on hydropower engineering for accumulation body in reservoir area or dam site. A large-scale clastic accumulation body with grain size of 30–200 cm is distributed on the slope of a gorge. It is difficult to carry out strength test and stability evaluation for such an accumulation body. Taking Wunonglong large-scale accumulation body located in front of the damsite in middle-upstream of Lancang River as an example,the method to estimate the engineering properties of the accumulation body such as strength parameters and grain size distribution is introduced;and the stability analysis of this body is carried out. The results show that it is stable under natural conditions,and the safety factor is 1.11–1.15;under the action of seismic loading,considering that the internal friction angle is 36°–37°,the obtained safety factor is 0.98–1.02,which indicates that the accumulation body is stable. It is shown that the method adopted is proper. The method can provide references for the research of large-scale accumulation body and similar engineering.