Abstract: For permeability enhancement technology of high pressure water cutting coal seam, the effect of pressure relief in different coal (soft and hard coal), the corresponding slot number and the cutting depth were analyzed trough numerical simulation. The numerical simulation study was realized by three-dimensional finite element model established by the numerical simulation software FLAC^3D. The results showed that the released pressure and distortion range of soft coal were respectively about 1.8 and 2.6 times higher than hard coal's when the hydraulic cutting radius was the same. When the slot radius increased from 0.5 m to 1 m, the area of which pressure was 90% of the original and distortion range increased respectively to 1.56 times and 1.66 times. The drilling pressure relief and the deformation range of coal increased significantly which were caused by the mutual influence emerged between the slots, the hydraulic coal cutting area presents the overall pressure relief. The error range is 0.46% to 9.84% when the released range of the numerical simulation was compared with the results of theoretical formula, it shows that it is reliable to use numerical simulation to study the effect of permeability enhancement of hydraulic cutting.