The collinsion occured between gas molecules and pore walls causes the gas slippage phenomenon when gas flowes at low velocity in tight porous media. The phenomenon depends on the constructure of the porous media and mean free path of gas molecules. It results in that gas permeability is larger than absolute permeability of porous media and causes deviating off Darcy's law in low pressure. The gas flow quantity is governed by weighted addition of viscous flow and slippage flow. The distribution according to...