<p>A high-speed riverbank landslide entering the water can pose a great threat to public facilities and the lives of residents on both sides of the riverbank. Therefore, the precise calculation of riverbank landslide speed is very important for disaster assessment. Water resistance is one of the key factors affecting the speed of riverbank landslide. In order to quantify the resistance calculation of reservoir bank landslides and further provide experimental data and a theoretical basis for the analysis of the velocity of reservoir bank landslides, this study has developed an experiment to investigate the water resistance coefficient. The experiment features a water tank, a sloped section, and a smooth section. The sloped section is designed to accumulate kinetic energy in the landslide before it enters the water, while the smooth section is used to study the water resistance coefficient. Based on the dynamic and kinematic equations for underwater test blocks, a model for calculating the comprehensive water resistance coefficient has been established. The experimental results were analyzed through dimensionless methods, examining the impact of various dimension-less factors on the water resistance coefficient. The model for calculating the comprehensive water resistance coefficient was derived from multiple regression analysis. The theoretical formula for water resistance coefficient has a fitting degree of 0.77, indicating good accuracy. The study has proposed a sophisticated model for calculating the water resistance coefficient, enhancing the understanding of this coefficient. This advancement enhances the precision of predicting the inflow velocity of landslides into reservoirs, thereby improving the predictive accuracy of tsunami models triggered by such landslides.</p>