Karst slopes are characterized by shallow soil layers and a rapid surface-groundwater hydrological response, leading to complex runoff characteristics. While previous studies have examined surface runoff, soil-epikarst interfacial runoff, and epikarst runoff in karst slopes, they have largely overlooked the effect of lateral dissolution fissures between rock layers (interlayer fissures [ISFs]) on runoff characteristics. In this study, we simulated the number and thickness of ISFs through an indoor controlled experiment and then analyzed the influence of ISFs on karst slope runoff processes. The results indicate that in the absence of ISFs, the vertical dissolution fissure runoff (35 %-52 %) is the primary runoff component. However, as the number of ISFs increases, the interlayer fissure runoff gradually becomes the primary runoff component (20 %-78 %) and the onset of surface runoff is delayed. The presence of ISFs significantly reduces the runoff through vertical dissolution fissures. In addition, the number of ISFs is significantly negatively and positively correlated with the soil-epikarst interfacial runoff and interlayer fissure runoff, respectively (p < 0.05). These findings highlight the critical regulatory role of ISFs in karst slope runoff processes and underscore interlayer fissure runoff as a key component of runoff on karst slopes.