Keeping injection water well compatible with rocks and fluids in sandstone oil bears is very important for reservoir pressure maintenance during waterflooding. The quality control program of injection water is as being very necessary in protecting formation or preserving the injectivity of wells. In this study, a comprehensive laboratory and field studies were carried out at Rongxingtun oilfield to identify the causes for rapid injectivity decline and to find out remedial treatment methods to improve the water injectivity. Based on analyzing and evaluating damage characteristics of injection water on reservoir core plugs, the new remedial techniques called swelled clay constriction and salinity-gradient-water injection were proposed to prevent the injectivity from declining. The new specifications and quality guarantee system of injection water had also been established. The field test results showed the new salinity-gradient-water injection and swelled clay constriction techniques are effective to improve the well injectivities. Useful classifying criteria according to different characteristics of formations about water quality specifications had been established. A window-based software for operation and management enhancement of water injection system had also been developed.