Abstract: Darcyformula is not valid for flows in low permeability reservoirs, due tothe obvious non-linearcharacteristics of the flows. Based on the experiment data of low permeability core,a non-linear formula with two parameters is proposed in this paper.Combining with the Buckly-Leverett formula, non-linear displacementformula is obtained. From the solution of the displacement formula, iscompared with the linear flow, it is seen that the displacementefficiency of non-linear flow is lower, the water cut is higher with the same s_\rm w, especially, and thepressure gradient is bigger, which means the higher injection/productionpressure difference. So, smaller well distance and higherinjection/production pressure difference are needed for effectivelydeveloping low permeability reservoirs.