Abstract：Aimed at the structure characteristics of the slope at the IV–VI ridges on the left bank of the Yalongjiang River in Jinping First Stage Hydropower Station，such as the existence of deep fractures in the slope and the thin anti-sliding rock masses at the toe of slope，it is found that the possible boundary conditions，which control the underlying slope deformation or failure，may be comprised of the fault f9 and the larger deep fractures(SL15，SL13，etc.). Then the deformation and failure mode of the slope is indicated. Subsequently，based on the examples of slope instability induced by atomized rain in several hydroelectric projects，it shows that the key point，which is one of the basic ways having influences on the slope instability by the flood discharge，is the filled water in deep fractures，from which the saturation in slope will gradually arise. With the sensitiveness analysis of the static stability coefficients in the ultimate equilibrium state under the different water level conditions in the slope，the elementary results indicate that the slope stability problems will be comparatively serious. And the stability coefficients most possibly be difficult to satisfy the stability demands of the engineering slope design in the IV–VI ridge positions when the flood is discharged. So the corresponding engineering treatment measures must be adopted.
