Due to the decline of formation pressure in the middle and late periods of low permeability reservoir development, the development effect deteriorates. Therefore, it is essential to restore and maintain reasonable formation pressure. Based on the two-phase fractional flow equation in low permeability porous media, we consider the flow characteristics in reservoirs with threshold pressure gradient and the influence of formation pressure on oil viscosity. By applying the material balance equation, we deduce the theoretical formula of future cumulative oil production with different formation pressures. In view of the contradictory relationship between cumulative oil production and water cut increasing rate, and we construct a bi-objective function to evaluate the reasonable formation pressure. Results show that during transition process from current formation pressure to reasonable formation pressure, when the reservoir formation pressure maintenance degree is 0.88, it can ensure that future cumulative oil production is relatively large and water cut increasing rate is relatively low. Under the condition of the same formation pressure maintenance degree, as threshold pressure gradient grows, the impact on cumulative oil production gradually increases. In order to provide a good development result, the formation pressure should be recovered as early as possible before it drops significantly. This method can be used to calculate reasonable formation pressure quantitatively and provide a reference for high efficiency development in low permeability reservoirs.