Abstract: With increased mining depth, most coal mines will face the threat of high pressure groundwater. Bearing mining has already became a coal mining method commonly employed in China's deep mines, one of the key problems in coal mining above confined aquifer is how to determine the depth of destroyed floor due to mining influence. According to the relevant study of the depth of the broken floor during mining seam No.5 in Dongjiahe mine, taking fully mechanized coal mining face No.507 of Dongjiahe mine as engineering background, this paper analyzed a method which combines the numerical simulation with theoretical calculation, dynamically reproduced the development and failure process of the whole floor strata, found that the maximum depth of destroyed floor was 10~11 m, while the testing data are compared with those from the in-situ measurement. The empirical formula for the relationship between the depth of destroyed floor and equivalent length of combined coal face and buried depth were obtained. The results may be used to guide practice with similar water prevention work of a working face of bearing mining and design of the water control method, and also provides scientific and theoretical basis for forecasting and prevention of water inrush from the floor in Dongjiahe mine.