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Surface runoff on karst is a multifactorial hydrological process. There are a great number of studies focusing on rainfall-runoff from karst slopes on a large scale, but microscale studies related to soil-rock geomorphic units have been rarely reported. This study used rock-soil runoff plots on uncultivated land as a new form of natural rainfall catchment, and the yield of surface runoff was measured during four different rainfall events. Through monitoring rainfall runoff by soil-rock runoff plots under different rainfall events, it has been proven that the coefficient of surface runoff measured on uncultivated land of a karst area is very small compared to that of non-karst areas, only ranging from 0.0145 to 0.0408 in the measurement period. And multiple regression analysis showed that the rocks contributed less to the yield of surface runoff than the soils, and with the increase in rainfall, the contributions of both showed an increasing trend. The calculated surface runoff yield produced by soils showed a positive relationship with soil bulk density and a negative relationship with soil porosity, soil hydraulic conductivity, and root biomass, and the significance increased with rainfall, which was consistent with previous findings and demonstrated the accuracy and efficiency of the proposed method in our study. These study results contribute to a deeper understanding of the rainfall-runoff process in rocky desertification areas, and the proposed method of soil-rock runoff plots provides a new way to estimate the yield of rainfall runoff on the complicated geomorphic units of karst slopes.