Abstract: Falling off and cracks occurred to the pin roll of a engine manifold bracket during use. The fracture reasons for peeling off and cracks of the pin roll were analyzed by means of macroscopic and microscopic fracture analysis, metallographic examination and structural analysis. The results indicate that:under the vibration stress of the engine, fatigue cracks appeared at the welding spot of the bracket and the pin roll, and then resulted in the falling off of the pin roll of the manifold bracket; the reason of the falling off was the unreasonable structural design and joint technology and the low welding strength.