Abstract: By means of site explosion location and wall temperature curve inspection, macroscopic inspection,chemical composition analysis, metallographic test, hardness test, oxide skin thickness measurement and mechanical properties test, the tube-bursting cause of T91 three-stage superheater tube in supercritical tower boiler was analyzed. The results show that the tube-bursting is due to the original processing defects on the inner wall of the tube that resemble straight channels, during the operation, the original defects expand and extend under the internal pressure, which cause the tube to burst.