Abstract: By analysis of pore volume change caused by clay mineral swelling, the dynamic model for characteristic parameters of pore microscopic structure is developed. The relative permeability under different clay contents and water invading time is simulated using 3D pore network model for the purpose of quantitative evaluation of the influence of water sensitivity on relative permeability. The experiment indicated that in the process of development of loose sandstone gas reservoir in Sebei gas field, the invasion of formation water may causeclay mineral swelling, affecting the fluid percolation and flowing characteristics in the reservoir. The relative permeability curve will shift to the right and the seepage zone of the two?phase fluids will become smaller, and the influence of formation water on the reservoir is greater than that of clean water