Abstract: Improving injection water quality and controlling water profile of medium to low permeability layers can enllance oil recovery. This paper introduces a JKLQ - 25 fine filter which can be installed in wellhead to improve injection water quality. Field applications in 92 wells resulted in an average mechanical impurity removing rate of 60.2% and an average oil removing rate of 65.32%.The average water injection per day went up from 69.2% to 97.8%, yearly cumulative increamental water injection volume was 84, 520 m3 and the output value reached 5.2million. The input-output ratio was 1 to 5.47. This technology can meet the very strict requirements of medium to low permeability layers to itoection water quality.