The steam generator of Jinzhou refinery is head-floating steam generator w hose tube sheet was cracked after it was put into use in mo re then a year .The wide -area cracks in the tube sheet of oil slurry steam generator were found, and the cracks star ted from the tube bundles, and went along with the direction of radius.With the cor relation method, the metalloscopy method and the crack mechanics analytic method , the reason of the cracking on the CCU tube -plate was analyzed .The chemical components, mechanical proper ties , the appearance of cracks in macro and micro of the samples were analyzed .Experimental result indicates that both the chemical components and mechanical proper ties of the tube sheet meet GB6654 -96 , that is to say , material do not result in cracking o n the CCU tube -plate.Cracks meet the feature of stress corrosion.The generating and flowing of the stream induces pipe bundle vibration that becomes especially stronger under the action of g as -fluid two phase flow , which produces cyclic load on the welded joint of tube -plate and bring s fatigue broken .The conclusion is that an interaction between fatigue and stress corrosion is the reason of the cracking on the CCU tube -plate.Fatigue is the more important reason o f the cracking on the CCU tube -plate .The improvements of preventing cracks are put forward.