Abstract: In order to have the site measured data of the floor failure depth caused by the mining disturbances of the coal mining face,the data could be applied to the water disaster evaluation work of the coal mining face to prevent the water inrush from the floor of the coal mining face. Under the right underneath of No.21090 coal minin g face in Chaochuan Mine,there was-250 m east wing water drainage gateway and there were 7 monitoring and measuring boreholes drilled with an interval of 10 m and a vertical depth of 30 m. The ultrasonic technology was applied to monitor and measure the wave velocity of the floor strata with a period of 13 days. The results showed that the preparation and analysis on the monitoring and measured data of No.3,No. 5 and No.6 boreholes could get the floor failure depth of 23.36~ 24. 46 m caused by the m . ining disturbances of the coal mining face ,which was closed to the calculation results by the statistic formula of the floor failure depth stipulated from the mining regulations of seams under the buildings,railway and water body. When applied to the production,the data would be more reliable to the calculation data with the statistic formula and t hus the ultrasonic technology applied to detect the floor failure depth caused by the mining disturbances was feasible.