The interlaced underwater distributary channel sand bodies are developed in Chang 4+5 reservoir group in Jiyuan area，and their internal contact relationships are complex， which seriously affects the reservoir distribution law and water flooding development effect in this area. It is beneficial to the sustained and stable production and efficient development of Chang 4+5 reservoir in Jiyuan area by the fine study of identification and division of single sand body interface， analyzing the contact modes of sand bodes and their influence on water flooding effect in Chang 4+5 reservoir. Based on the identification and division of the single sand body interface， the core， logging， and dynamic production data are comprehensively applied to delineate the internal contact relationships of sand bodies， and then clarify the influence of transverse cross and vertical superposition relationships of sand bodies on water flooding effect. The results show that there are three vertical superposition relationships of sand bodies in Chang 4+5 reservoir in Jiyuan area， namely cut-stacked， superimposed， and separated. Among them， the cut-stacked sand bodies are more homogeneous，with high oil content and percentage of producing reserves under water flooding， followed by the superimposed sand body. The lateral contact modes of single sand bodies can be divided into three types： isolated mode， docking mode， and side-cut mode. Different contact modes reflect the difference in interwell connectivity of channel sand bodies， which in turn affects the effective time of water injection in oil wells. The effective time of water injection in oil wells corresponding to the side cut mode is short，followed by the docking mode， and the effect of water injection in oil wells corresponding to the isolated sand body is not obvious.