The article explores the application of multiaxial fatigue criteria in precision mechanical parts machining. It delves into the causes and prediction of fatigue failure, particularly in gear machining, using multiaxial stress analysis and finite element analysis (FEA). Real-world cases from the aerospace, wind power, and rail transportation industries highlight how multiaxial fatigue criteria optimize machining processes and enhance component durability. The article emphasizes the importance of residual stress control, surface treatment, and advanced testing methods to improve fatigue life, providing key insights for both the present and future of mechanical parts manufacturing.