In view of the instantaneous fracture phenomenon of the gear shaft of the gear pump for aeroengine,the material metallographic structure,structural stress,and stress analysis of its key moving pairs were carried out.Combining theoretical analysis with experiments,it was determined that the main manifestation of the instantaneous fracture phenomenon of the gear shaft was fatigue fracture,and the influencing factors of the fatigue fracture of the gear shaft were clarified.Based on this,the key dimensions of the gear shaft mounting hole and the machining process were optimized.The results show that the stress near the mounting hole of the optimized gear shaft is significantly reduced,which can effectively improve the fatigue resistance of the gear shaft under alternating load.