Abstract: There are some depression areas and coal gangue dumps in many mine areas in China, which generally occupy and waste large-scale land. To fill depression with coal gangue, it can not only reduce coal gangue, but also make depression reclaim. By calculating the depth of depression, depression can be filled in advance before the coal below is extracted, which contributes to save the ground of coal gangue and to improve the construction quality of the filling. Furthermore, the filling thickness should be controlled strictly to avoid it too high or low. Usually, coal gangue includes some toxic substances, such as mercury (Hg), cadmium (Cd), lead (Pb), arsenic (As), fluorine (F) and so on. As for the direct and simple filling method, while the concentration of the toxic substances is over the allowable mark, the soil and water will be polluted by coal gangue. So coal gangue will be classified by the concentration of the toxic substances, and different coal gangue should be filled in depression with different methods in order to avoid secondary pollution.