Abstract: As weak structural planes in geotechnical engineering, argillized interlayers play a controlling role in slope stability due to their shear strength properties. Existing studies often analyze the effects of interface roughness or moisture conditions independently, while in-depth investigation into their combined influence remains limited. This study focuses on the argillized interlayer from a typical slope in Guiyang, Guizhou Province. Three types of bedrock interfaces with different fractal intercepts (A = 0.3918, 0.4059, and 0.4263) were prepared using 3D printing and concrete casting techniques. Interface shear tests were conducted using the KTL-IST type ring shear test system under two moisture states (natural and saturated) and normal stresses ranging from 100 to 400 kPa.The results show that under natural conditions, the peak interface strength increases significantly with the increase of fractal intercept: the peak internal friction angle rises from 35.00° to 47.73°, and the peak cohesion increases from 71.97 kPa to 103.39 kPa. The residual strength parameters are also affected by the fractal intercept, among which the residual cohesion shows nonlinear variation. Under saturated conditions, the peak interface strength degrades significantly; under a normal stress of 400 kPa, the peak strength attenuation rates corresponding to the three fractal intercepts are 11.19%, 24.26%, and 21.62%, respectively. Additionally, the residual cohesion after saturation exhibits a positive correlation with the fractal intercept, while the residual internal friction angle shows nonlinear variation.Furthermore, under saturated conditions, the shear stress–displacement curves exhibit regular periodic fluctuations, primarily attributed to intrinsic soil properties such as coarse particle distribution, grain size composition, and heterogeneous development of the shear zone. This study reveals the variation patterns of shear strength at the clay-filled discontinuity–bedrock interface under different fractal intercepts and moisture conditions, providing a foundation for further investigation into the shear failure mechanisms of such interfaces.