Abstract: The high pressure fuel pipes used in truck diesel engine cracked in service. The crack morphology and fracture surfaces of cracked fuel-pipes were observed by stereomicroscope and scanning electron microscope. The results indicate that the failure mode of all the fuel-pipe was fatigue fracture. The crack origin was originated from the micro-cutting marks on the internal surface due to grit-blasting for cleaning internal hole. The crack propagated from the internal surface toward the external surface under the circumferential tensile stress due to the operating oil-pressure in the internal hole to lead to fatigue.