Abstract: The soft interlayer in the dam foundation rock mass has a great influence on the stability of the dam foundation against sliding, thus the researches on its failure modes and constitutive model parameters are of great significance. The remolded sample is adopted for triaxial tests: the lower part is made up of clay and cement of 20% and the upper is made by clay, the interface is made into inclined planes of 0°, 30°, 45° and 60° and roughed to simulate the real interface characteristics. The test results show that the critical angle range of weak-interlayer samples with different dip angles is 58.3°~61.7°, when the inclination angle of the structural surface is in the range of the critical angle, the soft-interlayer sample is destroyed along the structural surface, otherwise the failure surface appears in the upper part of the muddy soil. Linear fitting of the triaxial test relationship curve of , and the results show that as the confining pressure increases, the initial tangential modulus and the corresponding peak intensity of the sample increases. According to the test results, the corresponding D-C model parameters are obtained and applied to the anti-sliding design of the dam foundation, and good results are obtained. The research results have a certain reference value for the anti-slip design of the dam foundation and the researches on similar soft-interlayer projects.