Engineering accumulation slopes, a special geomorphological unit resulting from human disturbances, are characterized by a large slope gradient, lacking soil organic matter, and loose surface structure, which drives the engineering accumulation body to be prone to intensive soil erosion under heavy rainfall. To explore the effect of gravel on rainfall erosion occurring on red soil engineering accumulation slopes, a series of indoor simulated rainfall experiments were conducted to investigate the runoff characteristics, sediment yielding processes, and erosion dynamic mechanisms of red soil engineering accumulation slopes with different gravel mass fractions (0, 10%, 20%, and 30%) under different rainfall intensities (1.0, 1.5, 2.0, and 2.5 mm/min). The results showed that:1) the stable runoff intensity varied as a decreased-increased tendency with gravel mass fraction increasing under the rainfall intensity higher than 1.0 mm/min, whereas it varied as an increased-decreased tendency under 1.0 mm/min rainfall intensity, and both reached extreme values at 10% gravel mass fraction (maximal value or minimal value). 2) Under 1.0 mm/min rainfall intensity, runoff flowed in the regime of subcritical flow during the whole test. The Freund number increased by 24.5%-87.8% because of the existence of gravel, and the gravel promoted the runoff to flow. However, under 2.0 and 2.5 mm/min rainfall intensity, runoff flowed in the regime of supercritical flow. The Freund number was reduced by 4.2%-13.0% because of the existence of gravel, and the gravel slowed down the runoff flow. 3) The erosion rate variation during the rainfall test was affected by the gravel mass fraction and rain intensity. Red soil engineering accumulation slopes became more vulnerable to rill erosion and gravity collapse under higher rainfall intensities and lower gravel mass fractions, resulting in multi-peaks and multi-valleys in the erosion rates.4) Under 1.0 mm/min rainfall intensity, the gravel exacerbated soil erosion with the erosion rate increasing by 28.7%-50.5%. On the contrary, the gravel retarded soil erosion with the erosion rate decreasing by 5.0%-64.4% under rainfall intensity higher than 1.0 mm/min. 5) The stream power could serve as the optimal parameter for describing the hydrodynamic process of the red soil engineering accumulation slopes. The values of erodibility-related parameters and the critical stream power values ranged from large to the small corresponding with the gravel mass fraction being 10%, 0%, 20%, and 30%, respectively. The results may provide a scientific basis for soil erosion control and erosion modelling for the red soil engineering accumulation slopes.