Abstract: Pai-2 unit of Chunguang oil field is characterized by'shallow buried depth,good oil properties,high productivity index and strong edge water energy'.Focused on reservoir numerical simulation technology,combined with the comprehensive research method of reservoir engineering,water cut change characteristics and rising reasons after water breakthrough of oil wells of Pai-2 unit have been analyzed.Through water cut change after control measures of water flooding wells,the water cut change regularities of thin oil reservoir with strong edge water have been made clear,and it provides technical support for the efficient development of oilfield.