Abstract: The cross universal joint for a hot rolling machine fractured at the position without high stress. The fracture reasons of the cross universal joint were analyzed by means of macroscopic observation, chemical composition analysis, mechanical property testing, metallographic examination and fracture analysis. The results show that:the main cause of fracture of the cross universal joint was the existing of voids and bulky non-metallic inclusions in the material, which resulted in crack source and fatigue cracking during reciprocating motion; the minor cause of the fracture was that a large number of non-metallic inclusions existed in the material, which resulted in the poor strength and toughness.