Abstract: In order to bring about balanced water displacement and enhance swept areal coefficient,an optimized model about injection-production pressure difference has been established according to breakthrough time equations of inverted 9-spot well pattern by assuming every breakthrough time of production well is equal.The rational ratio of △ps(differential flowing pressure of injection well and production well on the side)to △pc(differential flowing pressure of injection well and production well on the corner)is inversely proportional to the product of geometrical factor and reservoir seepage factor.Based on the practical production data of Ordos basin,calculation results have been given.It is concluded that the rational △ps/△pc is more beneficial to balanced displacement.