Abstract: Deep-buried,high pressure and low permeability reservoirs of Wendong oilfield have been taken as the research object.Through core experiment analysis of the change relationship between porosity,permeability and the stress sensitive effect,the change relationship between the permeability and starting pressure gradient has been determined.Experiments and simulation results show the porosity,permeability and stress sensitive effect should be changed as a power function.When the permeability is under 5 x 10-3μm2,there is an obvious start-up pressure gradient.With decreases of the permeability,the start-up pressure gradient increases sharply.The start-up pressure gradient has a linear influence on yield and the stress sensitive has an index effect on yield,which has a greater effect on capacity than that of start-up pressure gradient effect.