Slope topographic relief is an important factor affecting soil erosion. The relationship between surface roughness, sediment yield and hydrodynamic parameters is the basis for studying slope soil erosion process. The relationship between surface roughness and erosion characteristic parameters in slope erosion process in exposed Pisha sandstone area is studied by field in-situ simulated scour test and terrain factor parameters extracted by ArcGIS. The results showed that:(1) With the increase of scour intensity, the characteristic parameters of resistance decrease gradually, and the characteristic parameters of sediment yield and flow and other hydraulic parameters increase as a whole. With the increase of scouring time, Froude number showed a decreasing trend and other hydraulic parameters showed an increasing trend. The values of Reynolds numbers were all less than 500 under the three scour flow conditions, and the runoff was in laminar flow state. However, when the scour intensity increased, the Froude number showed the law of flow state from slow flow to rapid flow. (2) The change law of surface roughness was not obvious with the increase of scour flow. When the scour intensity was small (<100 L/h), the relationship between surface roughness and sediment yield characteristics was close. (3) Velocity had a significant power function relationship with surface roughness (R²>0.561), which is the optimal parameter reflecting the change of surface roughness. (4) Through Mantel correlation analysis, it was found that with the increase of scour intensity, the change of surface roughness will change from sediment yield characteristics to hydrodynamic parameters characteristics. The results are aimed to reveal the relationship between surface roughness and characteristic parameters of soil erosion process, and provide theoretical basis for the construction of slope soil erosion model in the exposed Pisha sandstone area.