Abstract: Abstract: North China Plain is the main coal production area with sedimentary deposit coal seam overlaid by the thicker soil layer above. The decrease of land surface elevation typically occurs at the rate in centimeters per year. Subsidence causes permanent inundation, especially topography gradient increase on the boarder of subsidence, surface runoff change, soil and water loss, and soil quality decline. It is critical to study the relationship among subsidence, surface runoff and soil quality change, and find the key factors that control the water and soil loss. In this paper, a two-dimensional undisturbed soil field experiment is performed, simulating subsidence process during coal mining. The data monitored in the experiment include surface subsidence, soil structure development, ammonia concentration and particle size change of soil during the rainfall-runoff process. Results show that underground mining not only changes surface topographic gradient and soil structure significantly but also aggravates the transport intensity of nutrient and particle in soil with runoff in the horizontal direction. Moreover, the soil crack produced by surface subsidence forms a series of groundwater preferential flow paths and promotes nutrient transport towards deeper layer. Firstly, in the horizontal direction, the ammonia content decreases by 14% on average in the subsidence with a length of 1.2 m and a slope of 2.1o after simulated rainfall of 122 mm. Secondly, in the vertical profile, the original ammonia peak value in the surface layer is 8.8 mg/kg, migrating a depth of 30 cm downwards. Thirdly, soil texture changes ununiformly in different subsidence parts. On the sloping bottom over the distance of 1.2 m, the fine-grained soil clay (≤ 2 μm) content decreases from 2.5% to 2.1%, and the average rate of soil clay loss is 16%; coarse-grained sand (≥50μm) increases from 3.2% to 3.8%, and the average increase rate is 3.6%. Reversely, the amount of clay at the bottom increases from 2.5% to 2.8% and the cumulative increase rate of clay content is 12%. This study shows that during the development of the subsidence basin, the soil crack experiences an evolution process of soil force changing from tension to compression. Preferential flow of soil crack has become an important driving factor for soil erosion in coal mining subsidence areas. In the tension stage of the crack development, the surface runoff would move deeper directly where the preferential flow paths are dominant. Part of the ammonia and soil particles in the soil would transport through these shortcuts with the runoff and infiltration. Furthermore, this process of crack preferential flow decreases the amount of lateral migration of soil nutrients and particles in the runoff and infiltration process and enhances profile transport. This process causes a rapid decline of soil fertility than usual. Fine particles move to the deeper layer and coarse particle proportion increases. The water and soil loss are strengthened. Therefore, the decrease of the quality of the soil caused by mining subsidence is completely different from the horizontal erosion type runoff erosion in the area where natural slope is predominant. Soil degradation caused by mining subsidence is more serious, and the soil crack preferential flow is the important driving factor to reduce the soil quality in coal mining subsidence area. It does matter to carry out control technology research for soil quality and improve the soil quality and land utilization efficiency in mining area.