Abstract: In order to obtain the failure features and failure depth of coal seam floor during the mining process, a site strain measuring method was applied to monit or and measure coal seam floor during the mining process. Different depth axial strain and radial strain variation curves of the floor were obtained. The failure scope an d depth of the seam floor were obtained from the analysis on the strain variation. A site strain measurement was conducted with seven strain sensors set in the floor of No.5304-2 coal mining face in a mine of Shanxi Province. The measurement results showed that the floor failure depth of the coal mining face was 14 m and the mining turbulence failure depth was about 12 m. During the mining operation process, the floor affected by the mine strata pressure behavior would have advance and delay fe atures and the influence scope would be reduced with the floor depth increased.