Abstract: Coking burst heating furnace tube in a xylene workshop with 20 steel after using 50 000 h had been comprehensively investigated by observing the microstructure and testing the mechanical properties at room temperature. Large finite element analysis software ABAQUS was used to simulate that the effect of coke layer thickness on the heat stress distribution in the furnace. The results show that the overtemperature happend on part of the tube because of coking, and resulted pearlite spheroidization, thus, the mechanical properties of the tube decreased, and the tube bursted at the combined action of internal pressure and heat stress.