Debris flows with a high concentration of solid materials and sediments can disturb sustainable environmental management, damage structures, and endanger human lives. Slit dams are one of the measures for debris flow control. In this study, laboratory experiments were conducted to estimate the discharge coefficient of slit dams’ outlets in two flow conditions involving clear water flow (without sediment) and debris flows (sediment condition). A set of factors, e.g., flow discharge, sediment discharge, slit width, upstream flow depth of slit dam, and viscosity, was selected as influential variables on the discharge coefficient. The Buckingham method was applied to extract dimensionless factors. Then, the discharge coefficient was estimated using linear and power regression analyses. The best equations for clear water flow and debris flow were selected using statistical indicators. Moreover, an equation was derived as the correction coefficient to consider the effect of sediment concentration. The results demonstrated that the discharge coefficient decreases due to increasing sediment concentration in debris flow up to 35%. Moreover, comparing the results of linear and power equations for both debris flow and clear water flow conditions revealed that power equations estimate the discharge coefficient more accurately and physically correct. Based on the proposed equation for the debris flow condition, influential dimensionless factors on the discharge coefficient respectively are relative depth, sediment concentration, and Reynolds number. The finding of this research will help estimate the discharge coefficient of the slit dams and decrease debris flows’ damages to natural and built environments.