Abstract: The fracture morphology, microstructure and chemical composition of an oil inlet bracket for engine was investigated using an ultra-depth 3D optical microscope, a metallographic microscope, a spectrometer, a carbon and sulphur analyzer, and a scanning electron microscope, and the fracture mechanism and basic cause were determined. The results indicate that during platform test, the U-typed notch near the bending section had a significant stress concentration, where the fatigue crack initiated at the root of overlap-typed surface defects and propagated under the periodic vibration stress, leading to the final fracture failure. By optimizing the structure design and controlling the machined surface quality, the performance of the bracket can be improved and such early fatigue failure can be avoided.