Abstract: Clay swelling is the main reason causing reservoir permeability reduction and water-injection pressure rising during waterflooding development of water-sensitive reservoirs. Though anti-swelling agents can be added to inhibit clay swelling and to reduce damage to permeability, water-injection pressure rising and insufficient water injection will occur in low permeability reservoirs. To achieve long-term and effective water injection and taking Wellblock Ji 7 for example, the study on anti-swelling technology for acidizing pretreatment is carried out for water-sensitive reservoirs. Compared with inorganic and organic anti-swelling agents, using acidizing pretreatment technology can get the minimum permeability loss, long-lasting and stable anti-swelling effects. Two injector groups with similar reservoir conditions in Wellblock Ji 7 are selected to carry out a contrast test. The results show that compared with the non-acidized pretreatment wells, the injectors with acidizing pretreatment before water injection are featured with low wellhead start pressure and slowly rising of water injection pressure, which can meet the demand of long-term water injection in low-permeability and water-sensitive reservoirs. Field applications of the pretreatment technology in 22 wells show that the technology can effectively slow down the rising of water injection pressure and good effects have been gained.