The first large scale dominant loess dumping area in China, South external dumping area of Antaibao open pit coal mine occurred failure on October 29, 1991. The volume of sliding mass was approximately 11 Mm3. The loss is 6 person’s lives and a huge wealth. After 1987, many large-scale open pit coal mines were established. Six open pit mining areas have loess distribution of total nine open pit mining areas. Large-scale dominant loess dumping areas are formed and will be formed in China. More effort must be implemented to control stability risks of dominant loess dumping area. A field investigation was carried out in East open pit coal mine. It is including geological overview, hydrogeological conditions, water content of waste loess, floor conditions of external dumping area, and stable problem statements. A series of experiments are conducted. Test results show that the density of waste loess increases as the water content increases. The Young’s modulus and angle of internal friction of loess decrease as the water content increases from 15% to 25%. The cohesive strength of loess decreases dramatically as the water content increases from 15% to 25%. In the working face, the water content of loess should be as low as possible to decrease the transport costs. In roads of dominant loess dumping area, the water content of waste loess should be maintaining a suitable value to promote the quality of roads. In the dominant loess dumping area, the water content should be as low as possible under the conditions that meet environmental protection and land reclaiming.