Carbonate reservoirs in Middle East are mainly porous. Water flooding will be a useful development scheme，and water flooding recovery is influenced by properties of injected water. Based on the core displacement experiments of carbonate reservoir in M layer of Middle East，effects of salinity and mass concentration of calcium ion and sulfate ion of the injected water on oil displacement were studied. The results show that water flooding recovery can be effectively enhanced and oil displacement can be effectively improved when the salinity and calcium ion concentration of injected water decrease and sulfate ion concentration of injected water increases. The oil displacement effect may be enhanced through the change of salinity and ion mass concentration of the injected water in the process of water flooding in the field. The experiment results can be used for guiding optimal selection and improving the source of injected water of carbonate reservoir in M layer of Middle East.