During exploiting the tight sandstone oil and gas reservoirs, the descent of pore pressure willinduce the virtual stress increase, which makes the formation rocks deformation and the porosity permeability descent. The theories and the deformation reasons  about  the tight sandstone are analysed from rock mechanics point of view in this article. With the virtual stress alteration, the tight sandstone samples porosity and permeability change rule has been studied by the stress sensitivity experiment. The result shows that the porosity volume and the fracture width change are the main issues of the tight sandstone deformation, the deformation types in tight sandstone oil and gas reservoirs are mainly about elasticdeformation and elastic-plastic deformation. The interior factors of tight sandstone result in tight sandstone deformation, such as grain's rigidity, contact and  cementation relationship between grains, the characters of fracture in tight sandstone, and so on. With the virtual stress increase, the tight sandstone porosity volume and the width of the fracture are compressed, the permeability of the tight sandstone decrease in much extent, which will lead to a serous formation damage.