Taking Chang8 reservoir in A83 area of Ordos Basin as the research object，a core displacement experiment based on the online scanning of nuclear magnetic resonance（NMR）was performed to explore the method of enhanced oil recovery（EOR）in tight sandstone reservoirs and solve the problem of low production of matrix during water flooding. Specifically，the process of dynamic imbibition between fractures and matrix in water flooding was simulated；the recovery of three types of pores was quantitatively evaluated regarding pore scale，and four factors affecting imbibition efficiency were analyzed. The results show that the process of dynamic imbibition of water flooding can be divided into three stages，i.e.，the stage of a rapid rise of recovery of the macropores under the displacement effect，the stage of a slow rise of recovery of the micropores under the imbibition effect，and the stage of basically reaching dynamic imbibition balance. In the process of imbibition，the recovery of micropores registers the largest，which is the main contributor to total recovery，and the recovery of the mesopores，flow channels connecting the micropores and the macropores，registers the smallest. To sum up，the whole process of dynamic imbibition is like an organism. For the maximization of the total recovery rate，it is necessary to control the injection rate（0.1 mL/min），surfactant concentration（0.05%），and soaking time（accounting for 75% of the total）. In addition，we should make the best use of the two oil recovery methods of the imbibition and displacement to ensure that the recovery of the micropores and macropores is increased as much as possible.