Pre-splitting blasting has been widely employed in river channel slope excavation to effectively mitigate damage to the retained rock mass, reduce blast-induced vibrations, and optimize blasting parameters for water-saturated slopes. Investigation of reasonable parameters for pre-splitting blasting in such conditions is important for river channel excavation projects. Based on geometric, physical, and dynamic similarity principles, an experimental model for pre-splitting blasting water-saturated slopes was designed, utilizing concrete as a substitute for red sandstone and detonators instead of emulsified explosives. The quality of pre-split crack formation, slope face shaping, and retained rock mass damage were evaluated under various conditions. The results showed that the pre-split crack formation quality and slope shaping quality significantly improved. The damage to the retained rock mass was reduced by 24.86% when the hole diameter increased from 0.8 cm to 1.2 cm. Field test results indicated that the optimal blasting effect can be achieved with a pre-split hole diameter of 115 mm and a hole spacing of 80 cm in a practical application of pre-splitting blasting for water-saturated slopes when the geological conditions involve medium-hard rocks.