Abstract: Analysis on stress sensitivity of tight reservoir rocks is of an important significance in accurate understanding of formation damage during oil?gas development and reasonable evaluation of oil?gas well productivity. In view of real situation of tight reservoir rock’s percolation changes resulted from stress field unsteady state change by waterflooding process, three types of typical rock samples (argillaceous siltstone, siltstone and medium?fine grained sandstone) of Yanchang formation in Ordos basin are used to make a measurement of the stress sensitivities of the tight reservoir permeability, and conduct correlation of the features of stress sensitivity from the three types of rock samples by means of linear fitting equation. Meanwhile, the influences of the rock constituents and microstructures on the stress sensitivity are analyzed comprehensively. Results show that with effective stress increasing, the argillaceous siltstone’s permeability decreases quickly,and its stress sensitivity is strong; the siltstone’s permeability decreases in medium range, and its stress sensitivity is medium to strong;and the medium?fine grained sandstone’s permeability decrease slowly, its stress sensitivity is weak. Through core, thin?section, SEM,whole rock X?ray diffraction analyses and mercury injection experiment, it is suggested that the stress sensitivity features of the tight reser?voir rocks are mainly influenced by two key factors of the mineral constituent and pore structure, while micro?cracks in the reservoir rocksare of the largest effect on the stress sensitivity