Abstract: Abstract： In order to research the damage rule of mining floor with a coal mining, this paper make a analysis about the damage depth of mining floor by respectively using test method of the bottom of water injection test, rock strain detection and theoretical analysis. Basing on the test site, it is found that the first mining failure appears in the mining floor when the floor pushes to the measuring point and the damage depth is about 18.5m. The damage depth of floor strata deepens to 18.5m to 19.5m when the floor pushing over the measuring point is about 15m~20m. Elastic theory calculated that maximum damage depth of mining floor is related with the seam depth H, the stress concentration factor n, the uniaxial tensile strength of rock Rt. The maximum damage depth of mining floor increases with the seam depth and the support pressure increases, and decreases with the uniaxial tensile strength of rock decreases. The damage depth of mining floor in water injection test, rock strain detection and theoretical calculation is both about 19.5m on the test site in F6106 working face. The three methods can accurately predict the damage rule of mining floor in BuLianGou coal mine no. 6 coal seam floor.