Separate layer water injection is an effective measure to weaken interlayer interference and alleviate the interlayer inconsistency. Sectional water injection is a common approach used in reservoirs with multi-layer in the vertical by combining layers with similar physical properties. The layers were classified according to the differential absorption index as the dividing standard. Based on Buckley-Leverett displacement theory，the method of calculating the water allocation of each section was established to achieve equilibrium displacement. Calculation program was made and verified by numerical simulation model. The result shows that the differential absorption index is a scientific dividing standard，and the injected water distribution is influenced by reservoir physical property，residual oil saturation and adjusting time. As the extension of adjusting time，the difference of injected water quantity between sections becomes smaller and the water saturation rises when the equilibrium reaches. Larger average water saturation in sections brings smaller water allocation for unit thickness. With the increase of differential absorption index，the required quantity of water for unit thickness decreases gradually.