Abstract: The nature and cause of massive fracture of stainless steel tube bundles of four heat exchangers of a petrochemical oil refinery work were analyzed by means of macroscopic examination, metallographic examination, fracture macro and micro analysis and energy spectrum analysis. The results show that the fracture of the stainless steel tube bundles was caused by corrosion fatigue cracking from outer wall to inner wall under the action of alternating load and corrosive medium, the corrosion fatigue cracks started from the outer wall corrosion pits, and Cl- and H2S in outside medium of the stainless steel tube bundles accelerated the propagation of the cracks. The cracks first propagated in corrosion fatigue mode, then continued to propagate in stress corrosion mode, and finally fracture happened when the crack propagation reached to fracture strength of the tube bundles. At last, measures and suggestions to prevent fracture were put forward.