The jet trajectory and scour characteristics of a narrow slit-bucket with different shrinkage ratios in an asymmetric river channel were examined via model test of a hydropower station. The findings demonstrate that the shrinkage ratio of the narrow slit-bucket significantly influences the morphology of the scour pit. As the shrinkage ratio decreases, the sidewalls of the bucket constrict the water flow, while the jet disperses more effectively in the air, thus increasing energy dissipation, and consequently resulting in a decrease in scour pit depth and an increase in scour extent. For asymmetric riverbeds, the scour depth amplifies with an increasing β value at a given flow rate. However, the lateral spread of scour notably reduces. Furthermore, a comparative analysis was conducted to calculate the jet trajectory. The results reveal that the calculation result of Chen Zhongru’s formula agrees well with test values when shrinkage ratio (β) is greater than 0.2. When β=0.2, the modified formula from the hydraulic calculation manual proves to be a better choice for calculating the jet trajectory.