The pore structure of He8 reservoir in eastern Sulige Gasfield of Ordos Basin is complex，and the study on seepage laws is relatively weak. It is difficult to evaluate the reservoir quality by conventional methods. Therefore，techniques of casting thin sections，scanning electron microscope，rate-controlled mercury penetration，nuclear magnetic resonance and microscopic waterflooding model based on real sandstone were used to study microscopic pore structure and influencing factors on movable fluid saturation. The results show that the types of reservoir space are mainly residual intergranular poreintercrystalline pore，intercrystalline pore-debris dissolved pore and microcracks-micropore，and their development degree successively decreases and their physical properties become worse in order. The reservoir seepage capacity，oil isplacement efficiency，mine recovery and movable fluid saturation also decrease successively and the corresponding oil displacement pattern changes from homogeneous network-like flooding to finger-like flooding. Nuclear magnetic resonance data show that the average saturation of movable fluid in He8 reservoir is 39.16%，and the types of reservoir are mainly II，III and IV. The movable fluid saturation is positively related to porosity，permeability，residual intergranular pore face rate，average throat radius，effective pore volume and throat volume，and it is negatively related to pore throat radius ratio.