A reasonable layering method of a water injection oil reservoir comprises the steps: S10, establishing a plurality of typical injection-production well group models; S20, performing numerical simulation of multi-layer commingled injection; S30, drawing a Lorentz curve according to the simulated cumulative percentage and yield cumulative contribution rate of each layer of reserves before water breakthrough; drawing a Lorentz curve according to the cumulative percentage of reserves of each layer after water breakthrough and the cumulative contribution rate of the yield to obtain Lorentz coefficients before and after water breakthrough; S40, calculating equilibrium displacement criteria before and after water breakthrough; S50, introducing an LSTM neural network to carry out simulation rationality supervision to obtain a final equilibrium displacement criterion threshold value; and S60, judging the layering rationality of the well group. According to the invention, the Lorentz coefficientis introduced as an evaluation standard, the water breakthrough time level difference of each layer before water breakthrough and the water content rise rate level difference of each layer after water breakthrough which comprehensively consider each dynamic and static factor are taken as economic and technical boundaries of layered water injection. The situation that injected water is not evenlydistributed in the longitudinal direction is improved, the accuracy of oilfield flooding stratification evaluation is improved, the flooding utilization rate is increased, and the method is an effective measure for improving the flooding effect.