Abstract: Injection- production ratio in some offshore oilfield of Bohai is less than one,the stratum energy can't be supplied efficiently,layer pressure drop to below bubbling pressure. The development mode between high water flooding and depletion is defined as half depletion development.The concept of injection/production ratio has been induced under the definition of stage remaining rate and water flood index.Based on Tong standard correction water flooding curve and material balance rule,a set of new method to evaluate half depletion water flood developing effect has been established.Actual examples show that this method is applicable,easy and practical,overcome the defect of complicated calculation. The actual data change trends indicate the following comprehensive adjustment direction and time of the oilfield.