Abstract: During the operation of a sulfur recovery unit, the reactor cracked and the medium leaked. The cracking causes of the reactor were analyzed by means of macroscopic analysis, chemical composition analysis, metallographic analysis and fracture analysis. The results show that the structure design of inner wall baffle of the reactor was unreasonable, which led to the stress of the connection between the reinforcing angle steel and the reactor wall. Under the action of periodic ventilation of air, the reactor wall occurred fatigue cracking.