CBL cracking furnace independently designed by SINOPEC is adopted in an 800 kt/a ethylene plant. The cracking furnace has run smoothly since the first startup, but over temperature and carburization of some furnace tubes has been found. The analysis shows that the reasons for the damage include the poor quality of feedstock, the distortion of outlet temperature indication of radiant tube, and the overheating during decoking. These problems were solved correspondingly, and the damage ratio of furnace tube was reduced significantly.