Abstract: The relationship of sheet-flow erosion and hydraulic factors on tapered engineering spoil bank slopes was investigated by laboratory simulation of scattered, tapered spoil banks in the red soil region of northern Jiangxi Province, China. An artificial rainfall experiment was conducted using a complete combinatorial design of four rainfall intensities (1.0—2.5 mm/min) and three gravel contents (10%—30%). Gray relational analysis was performed to assess the correlation between hydraulic parameters and soil detachment rate on the spoil bank slopes. The results showed that: ① Under the experimental conditions, there was a power function relationship between stream power and soil detachment rate; ② With a fixed gravel content of spoil bank, the analysis with rainfall intensity as a variable could reflect the correlation between hydraulic parameters and soil detachment rate on the spoil bank slopes; ③ Under a fixed rainfall intensity of greater than 1.5 mm/min, it was unsuitable to use the gravel content of spoil bank as a variable of gray relational analysis. In conclusion, stream power is the optimal hydraulic parameter to describe the erosion process of tapered engineering spoil banks, and it can be used to construct physical models of spoil bank erosion in the red soil region of northern Jiangxi.