Experimental study was carried out to quantify clay mineral and corresponding reservoir sensitivity of Chang 8 ultra-low permeability formation in Wuqi Area, Ordos basin. Thin sections were prepared out of core samples, while corresponding analyses were respectively performed by using the scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The composition and relative contents of clay minerals were identified. Subsequently, core samples flow experiments by injecting different synthetic brine were performed to evaluate reservoir sensitivity. The content of existing four main clay minerals, i.e. illite-montmorillonite mixed-layer, kaolinite, illite and chlorite, is 47%, 25%, 15%, 14% respectively. The physical property of reservoir is positive correlation with the content of chlorite, but is negative correlation with the content of illite and illite-montmorillonite mixed-layer. The differences of the morphology, properties and content of clay mineral cause the weak-medium weak velocity sensitivity, medium strong-strong water sensitivity, strong-extremely strong salt sensitivity, weak-medium weak acid sensitivity and weak-medium weak alkali sensitivity.