Abstract: After years of waterflooding, the total water cut has grown up to 70% in the Weizhou A Oilfield. It is urgently required to carry out researches on the dynamic changes in reservoir parameters during water-flood process for future development and production. Through a series of reservoir microcosmic experiments, we made a comparison of the reservoir parameters before and after flooding for the reservoir of same lithofacies. Mechanism analysis based on geological background was also carried out. It is concluded that, waterlogging may result in obvious deterioration of reservoir properties, such as strong heterogeneity in pore throat structures, increase in pores and moldic holes, decease in mud content and changes of clay in both content and type; during flooding process, the main factor for the changes in reservoir property is the production and precipitation of barium sulfate crystals, followed by hydration, expansion, dispersion and migration of clay minerals. As the injected water does not match well with the formation water, barium sulfate crystals crystallized and precipitated, eventually clogged up the throat and led to poor physical properties.