Water flooding effect evaluation in offshore oilfield has not formed a complete and mature evaluation system and industry standards currently. It is necessary to establish a set of flexible water flooding evaluation system based on the characteristics of offshore oilfield development. Differences and similarities of the water flooding characteristics of the offshore and onshore oilfields were analyzed. A set of commonly used water flooding evaluation indicator system was established focusing on oil production and production rate. Evaluation indicators were primarily selected based on the principle of independence，dynamic and operability. According to 25 samples from the typical offshore water flooding reservoir，importance of these indexes in water flooding evaluation was ranked using method of principal component analysis. Finally，10 key indicators were screened in aspects of recovery，energy，production，water flooding condition and water flooding effect，which provide favorable guidance for scientific evaluation of the water flooding effect in offshore oilfield. The indictors include control degree and produced degree of the water flooding reserves，pressure support level，cumulative injection-production ratio，yearly injection-production ratio，natural decline rate of yearly oil production，oil production rate of remaining recoverable reserves，raising rate of water cut，water flooding index and recovery degree of reserves.