Based on the coal floor of concealed structure water, bottom igneous rocks rich water, etc., which posed great threat to coal mine safety in production, in order to promote the further understanding of coal mine water hazards, took detection of Hengjian secondary orbital floor down coal mine water as an example, the basic principle and method of downhole high density characteristics were explained. On this basis, the high-density electrical method in coal mine underground roadway detection application effect of bottom water was expounded.