Abstract: The fracture reason of a link chain of 1 000 WM ultra-supercritical boiler slag conveyor was analyzed by means of physical and chemical testing and ANSYS finite element analysis. The analysis results of visual inspection, SEM and metallography show that some inclusions are found on the fracture surface, and the fracture mode is fragile fracture. The hardness of chain core is 371HB, and annular cracks are found at the edge transitional region of carburized layer. The results show that the chain fracture is caused by the improper heat treatment, leading to the chain fracture at stress concentration zone in the later service process. The finite element analysis shows that the maximum stress of chain during running occurs at the transition region of straight edge and circular arcs, which is consistent with the actual crack condition.