Abstract: After the oil reservoir being water flooded for a long time, its reservoir structure is changed based on laboratory tests and field data. This paper studies the rule of the changes about our model oil field thor-oughly by studying the data of geology, well logging, testing and production performance from the aspects of basic characteristics of the reservoir. The variation of the pore structure is studied. The result of the study shows that the changes of permeability and porosity of the reservoir is linked to the originality environment. The pore type has been changed, also the sensitivity minerals. The main reason of the changes is described at last. It is very useful for the other oil field.