Abstract: A new approach to determine oil recovery in low permeability reservoirs was introduced in this paper. Firstly, through the normalization of relative permeability curve and utilizing Darcy law, relationship between productivity index and water cut was established. Secondly, ultimate water cut can be obtained through economic limit oil production of single well and ultimate producing pressure drop of the reservoir. Finally, recovery efficiency has been calculated using the volume of water flooding and reservoir mercury ejection efficiency. The successful application of this method to low permeability reservoirs showed it had scientific significance to determine oil recovery rate in low permeability reservoirs.