At present，the main oilfields in eastern China are in the ultra-high water cut development stage，and the inefficient and ineffective circulation is very serious. The treatment of a large amount of produced fluid leads to a sharp increase in production and operation costs. The main technical indicators of reinjected sewage are often difficult to meet industrial requirements. Residual polymers，crude oil and suspended solid particles in the sewage are bound to cause plugging damage to low-permeability zones of the reservoir. In order to clarify the permeability limit of reservoirs for sewage reinjection and establish methods to improve the reservoir adaptability of sewage，the reinjected sewage and reservoir physical properties of XSG Oilfield were taken as research objects，and an experimental study on reservoir adaptability and improvement measures of reinjected wastewater in ultra-high water cut oilfields was conducted. The results showed that the oil content，suspended solid content and median particle size of reinjected sewage from the three under-injection wells far exceeded the industrial water quality standards. Retention and plugging of these substances in the pores of reservoir cores were the main causes of water well under-injection. The minimum permeability of the reinjection reservoir for sewage from Well 1 # was about 169 × 10^-3 μm²，and that for Well 3 # was about 103 × 10^-3 μm² . A n o p t i m a l blending ratio of sewage to fresh water could increase the Zeta potential of suspended particles in the blended water，enhance the stability of suspended particles，improve the compatibility between suspended particle size and core pores，and reduce the degree of plugging damage to t he reservoir. From a techno-economic perspective，the reco mmended wastewater-to-fresh water ratios were 4 ∶ 6 for Well 1 # and 6 ∶ 4 for Well 3 #.