Based on reservoir properties，scanning electronic microscope，cast thin section and constant rate mercury penetration，this paper cam ed out quantitative analysis of micro—pore structure of tight sandstone reservoir．The result shows that Chang 7 reservoir in Ordos Basin is typical tight sandstone reservoir,the reservoir permeability is less than0．3 mD，the secondary dissolved pore is the main pore type and average pore radius is 1 62 m，and there is 130correlation with permeability；the average throat radius is 0．33 p,m and has a good positive correlation with permeability．and it is the main influencing factor of permeability；the pore throat radius ratio is large and the average value is 602；the big pore is controlled by small throat，which causes reservoir strong heterogeneity and poor permeability．So，the advanced stimulation technology need to be used for large scale development of tight sandstone reservoir，and need to enlarge the throat radius and lower pore throat radius ratio and improve the permeability．