Abstract: Small bore pipes, existing in a form of large quantities of instrument pipes, sampling pipes and vent pipes, often suffer mechanical vibration fatigue fracture. Vibration fatigue life is evaluated according to measured vibration stresses for GRE023 pipes in Unit 2 of Yangjiang NPP. Measured acceleration time history were double integrated into the displacement time history for vibration fatigue life analysis by finite element method, and key parameters for transient dynamic analysis were also determined, which lays an empirical foundation for vibration reduction of analogical structure. The analytical method can provide a reference for small bore pipe vibration reduction in NPPs.