After running for a period of time,the WC-Ni cemented carbide O-ring seal used in a nuclear main pump has more cracks on the end face of the seal ring.In order to study the damage failure reason of the WC-Ni cemented carbide O-ring seal,micromorphology analysis,white light interference test analysis,chemical composition analysis and surface residual stress test of the damaged area of the seal were carried out,the damage characteristics of the WC-Ni cemented carbide seal ring surface were discussed,and the service safety was assessed.The results show that the crack source is mostly generated at the junction of the sealing groove and the dam area.Most of the cracks are distributed in the dam area,and the damage degree in the dam area is larger than that in the gully area.There is oxidation in the crack zone,but the degree of oxidation is relatively mild,and the oxidation product is mainly oxide of W.The crack is mainly caused by the large stress difference between the gully area and the dam area of the seal ring.The crack volume is small and the damage is slight,so it will not affect the overall mechanical seal equipment in a short time.