The degassing of crude oil in the formation will increase the seepage resistance,which seriously affects the development effect of low permeability reservoirs.This paper takes a low permeability reservoir in Weicheng as an example,using steady state water flooding test method to explore the effect of oil viscosity change on the oil water two⁃phase threshold pressure gradient,and study the effect of threshold pressure gradient on the effective displacement pressure difference in low permeability reservoirs.The results show that the threshold pressure gradient increases with the increase of oil viscosity after oil degassing,which results in the decrease of effective displacement pressure difference between wells.When the injection and production pressure difference is small,it is difficult to establish effective displacement.At the same time, some countermeasures are put forward to deal with this problem.The research results are of guiding significance for the design of injection⁃production well pattern and the later adjustment in low permeability reservoirs.