Abstract：The coal seam floor¢s distortion and failure would be found being because of the change of stress state after coal seam mining. The failure laws of the coal seam affected by mining are different. The exact failure depth of the coal seam floor is the primary condition to forecast accurately the capability of the floor to hold up water for the coal seam having the danger of floor water. So using the practical observation methods to get the floor¢s failure depth and laws is a direction for the mine geophysical study. Many observation methods are studied to get the coal seam floor¢s failure depth in the past decade years. But the effective observation methods are less because of the limitation of technique. The floor¢s failure developing laws and characters can be gained by seismic wave CT combining with the detective section between bore and lane in the working face. It is shown that the failure laws are dynamic because the CT data collection and process are variable according to the mining schedule. Engineering practice shows that the seismic wave CT has notable effect on the failure depth detection of floor，and it has dynamic characteristic and better applicability.
