The soil-rock interface is a common binary geological structure in the remediation of rock slopes. Based on the fiber reinforcement technology, this paper studies the coupling stability between the fiber composite clay substrate and the bottom. Through the sliding friction test, the influence of moisture content, sisal fiber content and other variables on the sliding process of the soil at the contact interface is studied. Combined with the micro analysis, the improvement mechanism of sisal fiber on clay is explored. The main research results are as follows:(1) With the increase of moisture content, the average value of dynamic friction coefficient of the sample increases first and then decreases. The critical friction angle α increases to the maximum value first and then decreases with the increase of moisture content. When the moisture content of the sample is between the plastic limit and the liquid limit, there is an optimal moisture content value to maximize the dynamic friction coefficient and the critical friction angle, and the adhesion effect of the clay sample is the best. (2) With the increase of fiber content from 0% to 1.2%, the average dynamic friction coefficient and the critical friction angle of the sample increase first and then decrease. The addition of sisal fiber can effectively improve the sliding failure resistance of the sample, but the reinforcement effect will be weakened with the increase of fiber content. The coupling effect of fiber composite clay and acrylic plate contact interface is the best when the content of sisal fiber is 0.8%.