Abstract: For the problem that the slotting depth of water jet can not be accurately identified, water jet velocity distribution within the cross section of a two-dimensional plane was derived based on the law of conservation of momentum. And the change laws of water jet scouring coal and rock depth with time and water jet cutting influence scope are determined based on the jet water jet power and linear relationship of coal and rock erosion volume, waterjet flow pressure attenuation law and Mohr-Coulomb criterion. Meanwhile, we carried out the field test of bedding drilling slotting at 2^# coal seam 2472 wind roadway working face of a coal mine in the south of Sichuan, and comparatively calculated the water jet cutting depth and the maximum cutting depth. The results show that the maximum error of the theoretical value and the measured values from field test is 8.67%, 8.53%.