Abstract: For being able to increase the rate of penetration and decrease formation damage, gas drilling has become an effective approach for developing the low-pressure and low-permeability reservoir. In order to analysis the flow of the fluid when encountering reservoir during gas drilling, the coupled model of well bore flow and reservoir percolation is established based on the unsteady flow of compressible fluid and the percolation of the formation fluid. Combined with the boundary conditions and the initial condition, the numerical solution of the model has been discussed. In the end, the velocity and the pressure distribution of different working conditions have been analyzed. The results show that after the unsteady stage, both working conditions will become stable.