Abstract: Abstract: Various engineering accumulations, caused by all man-made activities during mining process, have resulted in serious artificial soil and water loss in the coal mine area because of great difference in material composition, slope structure and runoff and sediment characteristics from original landforms, which would make great potential risk for the mining safety production and the surrounding areas. Recently, researches begin to focus on artificial soil and water loss in project areas, however, mechanism of runoff erosion on engineering accumulation slopes is still unclear, especially hydrodynamic characteristics in the process of runoff erosion needs further study. Taking typical coal mine engineering accumulation as example, soil test method and field scouring experiment were conducted to study the runoff erosion characteristics and critical hydrodynamic conditions of engineering accumulation slopes in the coal mine area. In this paper, some physical properties, hydraulic properties and runoff erosion process on slopes of engineering accumulations with different producing sources were all comparatively studied. Field scouring experiments were carried out from July to August 2013 at the Soil Erosion Experiment Site for production and construction projects in Southwest University, Chongqing. The field scouring experiments contained 5 flow discharges (i.e. 10, 15, 20, 25 and 30 L/min) and 4 slope gradients (i.e. 25°, 30°, 35° and 40°). The paper mainly studied the hydrodynamic characteristics of engineering accumulation slopes in order to reveal the characteristics of runoff and sediment yield and soil erosion rate, and to analyze the relationship between soil erosion and critical hydrodynamic conditions and the critical slope gradient under different flow discharges. The results indicated that: 1) During runoff erosion process, both flow velocity, flow shear stress and runoff power of engineering accumulation slopes exhibited different degrees of fluctuation, showing a range of 0.187-0.526 m/s, 24.336-126.542 Pa and 2.763-46.861 N/(m·s), respectively, however, resistance coefficient existed a fluctuation from weak to strong in the range of 2.236-19.337. 2) Both runoff yield rate and sediment production rate of engineering accumulation slopes exhibited a trend of first increase and then stability during runoff erosion process except for the 10 L/min flow discharge. The runoff yield rate tended to 0.5, 3.0, 3.8, 6.3 and 9.0 L/min, respectively, under different flow discharges (10 to 30 L/min), however the sediment yiled rate varied between 0 and 27.51 kg/min and the soil detachment rate changed between 9.570 and 4616.064 g/(m2·min). 3) There were great difference in critical flow shear stress and critical runoff power among engineering accumulation slopes with different slope gradients. At sheet erosion stage, both the critical flow shear stress and critical runoff power of 30° engineering accumulation were the minimum, whose values were 23.95 Pa and 1.76 N/(m·s), respectively; at rill erosion stage, however, the critical flow shear stress of 25° engineering accumulation was the minimum and the critical runoff power of 40° engineering accumulation was the least; and the soil erosion rate had a significant linear relationship with the flow shear stress and runoff power. 4) When flow discharge was 10-30 L/min, the critical slope gradients of engineering accumulations were 34.8°, 35°, 33.7°, 34° and 35.2°, respectively. These results not only could provide essential technical-parameters for predicting soil and water loss caused by mining production, but also would help to arrange some vegetation measures for soil and water ecological restoration of these engineering accumulations.