Abstract: The loess-mudstone interface landslide, as a kind of loess landslide, has the characteristics of double-layer heterogeneity, short slip distance and strong reactivity. Due to the low rate of deformation before the occurrence of landslides, it is often difficult to detect early, and it has caused serious damage when discovered. Research on the inducing factors and failure mechanisms of this type of landslide have been abundant. However, there are few studies on the loess-mudstone interface, especially the shear mechanical properties of the interface, and the influence mechanism of each factor on the shear strength of the interface is still unknown. Therefore, in order to investigate the influences of water content, dry density, and interface morphology on shear strength, cohesion, and internal friction of loess-mudstone interface samples, a series of shearing experiments were performed using a direct shear apparatus. The results show that as the moisture content of the loess increases, the shear strength of the interface first decreases slightly, and then decreases rapidly when the moisture content of the upper loess exceeds that of the lower mudstone. As the dry density of loess increases, the shear strength of the interface increases, but compared with the water content, dry density has a smaller effect on the interface shear strength. The influence of interface morphology on the shear strength is mainly reflected in the influence of the surface area of the undulating surface and the thickness of the shearing influence on the interface roughness. The deeply zigzagged interface has the highest shear strength and the smooth interface has the lowest under the same normal stress.