In order to accurately evaluate the integrity of cement sheath in fractured wells, the integrity failure evaluation experiments of cement sheath were carried out for fractured wells in Wushi 17-2 oilfield under the condition of alternating load, and the reason of integrity failure was analyzed based on the fatigue cumulative damage theory and failure criteria, and the integrity failure law of cement sheath under the condition of confining pressure 30MPa and alternating load was obtained. The result shows that:①Under the action of alternating pressure, the internal tissue of cement is damaged, and the mechanical properties of cement (such as compressive strength, etc.) decrease with the increase of alternating pressure cycles; ②The bonding strength of casing-cement interface is relatively small, and the plastic accumulation of cement sheath during the fracturing pressurization process leads to inconsistent strain at the interface of casing and cement, when the interface tensile stress exceeds the interface bond strength during pressure release, the interface separated and form micro-annulus. ③Under the condition of confining pressure 30MPa and alternating load, the primary failure of cement sheath is the micro-annulus, increasing the elasticity and denaturation ability of cement sheath is helpful to prevent the failure of cement sheath. The research conclusions can provide technical reference for the improvement of cement slurry and fracturing operation of fracturing wells in Wushi 17-2 Oilfield, and help to ensure the integrity of cement sheath of fracturing wells.