The rock masses of the sluice gate of the Datengxia Hydropower Station in Guangxi Province are selected in this study to conduct stability analysis by using Universal Distinct Element Code (UDEC) software. The investigated rock masses are composed of continuous soft layers with low dip angles as well as discontinuous structural fractures with high dip angles. The strength reduction method is used to determine whether the failure pattern is shear or compression type according to the displacement of key points, force imbalance, and plastic yield zone. The results show that the failure pattern of rock masses with continuous gently inclined and discontinuous steeply inclined unconformities is compression failure rather than regular shear failure. The reliability and rationality of this method are verified by comparing the results with those obtained by using a physical experiment model. Therefore, the results of the method proposed in this study can serve as a reference for similar engineering projects.