Abstract: The majority of water injection wells in Beibu Gulf oilfield are general water injection, and the complex fault block oilfields are vertical multi-layer, and the interlayer interference is strong. In order to accurately grasp the water injection situation of each layer, in this study, the material balance equation is studied in depth. In this paper, the material balance method is used to split the water injection volume of small layers, and it effectively improves the splitting accuracy of water injection in different layers. This method is a combination of dynamic and static and has a phased nature. It solves the the problem of large splitting error in traditional method, which provides an important basis for analysis of water injection efficiency, water injection allocation and potential analysis.