Abstract: The empty space in coal mines can not only destroy the minable seam and improve the cost of production, but also lead to water inrush, endanger the mine safety. For the various problems and potential security risks of coal mines brought by falling empty space, a new early warning method of empty space in coal mines is put forward to analyze the risk level of falling empty space, which is based on the dynamic tracing and fuzzy comprehensive evaluation. First of all, by means of the dynamic tracing, attributes of empty space like space sizes are extracted and its rates of change are also calculated. Then, a model is established by the fuzzy comprehensive evaluation method and based on the data of attributes and rates of change do the fuzzy comprehensive evaluation. Finally, comes to a conclusion of the risk level of empty space. Application experiments are operated to Dongshan Coalmine of Taiyuan and experiment results show that: the early warning method can effectively predict the risk level of empty space in coal mines in the practical engineering, and can also provide effective technical support for the early warning of cavitation diseases in mine engineering, the project reconstruction and treatment design.