Abstract:The aim of this research was to study the runoff process and total runoff characteristics of karst bare slope under different rainfall intensity and slope combinations. In this study, the caves and fissures in surface karst zone was regarded as a permeable "sieve hole". By setting the porosity (fissure) of the underground "dualistic structrue" structure to be the same (5%), the characteristics of surface/subsurface runoff process and total runoff on bare slopes under different rainfall intensity and gradient combinations were studied. Then, the effects of various factors on the hydrological characteristics of karst slopes were discussed. (1) Under the small rainfall intensities (15 and 30 mm/h), the runoff on bare slope was primarily dominated by the subsurface runoff without surface runoff. But, under the heavy rainfall intensity (≥ 50 mm/h), the surface runoff occurred, which process did not change regularly within 30 minutes of the designed rainfall; however, the subsurface runoff process increased first and then leveled off under all different slope and rainfall intensities, and the turning points were mostly in 9~12 minutes. (2) The differences of total subsurface runoff were not significant (P>0.05) in 5°, 10°, 15° and 20° slopes under the rainfall intensity of 15 mm/h in 30 minutes, while the surface/subsurface runoff had significant differences with the increase of slope gradients (P<0.05). All the surface/subsurface runoff was positively correlated with the rainfall intensities and slope gradients (P<0.01), except that the total subsurface runoff was negatively correlated with the slope gradients (P<0.01). (3) The subsurface runoff coefficient was less than 0.5 for the first time under the heavy rainfall intensity (90 mm/h), which proved that there was a critical gradient which made the surface and subsurface runoff equal to each other. These research results can provide reference and reasonable suggestions for the prevention and control of soil erosion in Karst slopes.