Abstract: The oil pipe fracture failure in a power plant EH governing system has been analyzed by mean of optical microscopy and scanning electron microscopy.The results show that the microstructure of the fracture surface is consisted of equiaxed grains,with the grain size of about 10-40 μm.They distribute homogeneously along the radial direction and has no obvious difference to the microstructure far away from the fracture surface.The observation of fracture surface show that there exist lots of fatigue cracks and also some welding defects and cleavage surface as well.The initiation of fatigue cracks originated from the surface,not from the welding defect or intergranular interface,indicate that the main reason for this failure is fatigue failure,and welding defects promoted this fracture failure.