Abstract: The reasons for fracture of the stretch-reducing roll being used to make the T91 steel tube at a certain domestic company are investigated,involving testing,inspection and analysis of such elements of the roll as chemical composition,microstructure,mechanical property,operation process and manufacturing process,etc. Relative countermeasures are also studied. As a result,it is revealed that in the material of the roll,the contents of chemical elements Mn,Cr,Ni and Mo are rather low,which leads to tensile strength deficiency of the basal body,and this is the internal reason for the said fracture;due to improper control of the heat treatment temperature and the cooling rate,pearlite and bull’s-eye graphite structure occur in the core part of the roll,which also causes strength reduction of the basal body;and the unusual growth of the stress during the operation process,and this is just the direct reason for the fracture. The countermeasures are regularized as criteria for manufacture,operation and maintenance so as to prevent recurrence of the said fracture.