Abstract: Starting from decline rate equation of water drive oilfield,combining with water cut rising rate equation and the relative permeability curve,the relationship expression between natural decline rate and water cut rising rate has been theoretically deduced under the condition of certain liquid quantity and certain production pressure difference so as to match up with the current law of water cut rising research results and relative permeability results.Under the conditionof fixed fluid volume,natural decline rate is in accordanc with the change rule of water cut rising rate.Under the con dition of constant production pressure difference,the natura decline rate is mainly influenced by dimensionless oil produc tion index,and presents three kinds of morphological charac teristics along with the water cut variance.