Abstract: Determination of starting pressure gradient is signifi- cant for economic and effective exploitation in low permea- bility reservoir.However,it's usually obtained by water drives cores experiments,theoretical model calculation, numerical simulation,well test analysis and so on.In con- clusion,these methods are simply considered from static aspects,without the consideration of adjustment and rec- tification by dynamic data of oilfield.Based on the theory of fluid flow mechanics and regularity of starting pressure gradient,the correlation between the pressure influence radius and time of the low permeability reservoir is de- rived by using the steady replacement method.In addi- tion,an expression by which the starting pressure gradi- ent can be determined was provided.The case study shows that this method is a more reliable and accurate ba- sis to be used for determination of starting pressure gradi- ent in low permeability reservoir.