Abstract: Based on field investigation, the processes of earth road regolith erosion were studied under indoor simulated rainfall. Results showed that the runoff initiation time for both regolith and earth road surface erosion decreased with the increasing rainfall intensity and slope steepness. With the increase in regolith thickness, the initiation time for earth road surface erosion lagged for 2-5 min. When the regolith thickness was ≤0.5 cm, the runoff rate turned to be stable at 2 min after runoff generation, and the average runoff rate increased with the increasing rainfall intensity and decreased with the increasing slope steepness. When the regolith thickness was ≥1.0 cm, runoff rate turned to be stable at 3 min after runoff generation, and the average runoff rate increased linearly with the rainfall intensity but exhibited a gradually decreasing trend after the first increment with the increasing slope steepness. The critical point for regolith erosion decreased with the increasing rainfall intensity and slope steepness. With the regolith thickness of ≤0.5 cm, the erosion rate increased with the increasing rainfall intensity, with the erosion rate ranging from 24.5% to 434.4%, and the erosion rates for 8° and 16° slopes were 2.4 times as those for 2° and 4° slopes. With the regolith thickness of ≥1.0 cm, the erosion rate turned to be stable about 9 min after runoff generation and increased with the increasing rainfall intensity and slope. With the increasing slope steepness,  the erosion form changed from sheet erosion to rill erosion and then to headward
erosion. The average erosion amount over 10 min single rainfall for the regolith thickness of ≥1.0 cm was 1.3 times as that for the regolith thickness of ≤0.5 cm, while it was 2.7 times as that at the stage of regolith erosion alone. With the regolith thickness of ≤0.5 cm, the erosion amount had a significant correlation with rainfall intensity, and runoff volume with slope steepness. With the regolith thickness of ≥1.0 cm, both runoff and sediment yields in 10 min single rainfall had a significant correlation with rainfall intensity. The proportion of regolith erosion to the combined erosion increased with the increasing regolith thickness, while the road erosion was the main form at small regolith thickness.