Abstract: The middling product of the rare coking coal heavy medium separation system of Huaibei Coal Preparation Plant is taken as the object to explore the characteristics of the middling product after proper liberation crushing. The size distribution and washability of the product and the feasibility of obtaining up-to-standard clean coal product. Test is also made on liberation crushing of the middling down to an upper size limit of 6 mm, 3 mm, 1mm and 0.5mm to analyze the density consist and liberation characteristics of the middling at different crushing sizes. Test results show that under specific ash conditions, the finer the crushing size, the higher the coal-mineral liberation level, and hence the higher the theoretical yield of clean coal; and when the middling is crushed down to a size with an upper limit of 0.5mm, the yield of clean coal is around 35%, which is 27% more compared with the figure before the middling is crushed. In overall consideration of the factors of consumption of grinding energy and complexity of subsequent separation and dewatering operations, the optimal crushing size is determined to be 0.5mm.