Abstract: The cracking reason of 1Cr18Ni9Ti steel furnace tube was analyzed by metallographic examination,mechanical performance test,ferrimagnetic phase content measurement,fractograph and EDS analysis etc. The results showed that there were PTA stress corrosion cracking on furnace tube inside wall and there were some stress corrosion cracking which was promoted by sulphide on furnace pipe outside wall. The proposal for avoiding cracking had been given.