Abstract: For extrude coal seam with soft coal， in order to inspect more accurate gas drainage effect， residual gas content diversity between soft and hard coal must be studied. Based on gas seepage field analysis of drainage conditions， considering the comprehensive influence of the condition of soft coal on gas flow and coal seam in coal seam， through establishing the gas fluid-structure coupling equation， and combining with the initial conditions and boundary conditions of borehole gas drainage， the differences of residual gas content of soft and hard coal under the extraction condition was simulated by using the multi-physic fields coupling analysis software. The results of numerical simulation showed the residual gas content of soft coal is higher than one of hard coal under the same extraction time. It will take 180 days when gas content of soft coal is reduced to 8m³/t， but it takes 162 days for hard coal.

Key words: gas fluid-structure coupled equations；residual gas content, numerical simulation；soft coal；borehole gas drainage