Abstract: Theoretical study shows the net stress is not equal to the effective stress because of the existing microcracks in the low permeability sandstone.In order to demonstrate the relationship between net stress and effective stress，laboratory work is performed in this study.The experiment includes the aging treatment and four times test on decreasing inner pressure at different confining-stress.The permeability data at all pressure points in the process of decreasing inner pressure is obtained with the steady-state method.The results show that permeability is different for the equivalent net stress in the different confining-stress，which implies net stress cannot take the place of effective stress to evaluate the stress sensitivity.At low confining stress，the variation range of permeability is wider，while at high confining stress，it is narrower.In the end，the stress sensitivity evaluation on permeability is done and the results show that the stress sensitivity is moderate sensibility for the studied tight sandstone reservoir.

Key words: effective stress, tight sandstone, net stress, micro fracture, stress sensitivity