Abstract: The interaction of ultrasonic-wave and leak-hole defect(s) in vacuum pipeline,to be filled with coolants and installed inside large-sized vacuum chambers used in nuclear/aerospace/chemical industries,was empirically approximated,mathematically modeled,theoretically analyzed and numerically simulated in finite element method with ANSYS software for non-destructive detection of hole-defects in pipeline walls.The influence of the interaction conditions,including the ultrasonic frequency,base-pressure,properties of pipe,position and size of hole-defects,on the acoustic signal distorted and reflected by the hole-defect(s) was investigated.The preliminary results show that a hole-defect,in an equivalent diameter of 2 mm,could be detected and localized with an axial accuracy of less than 2 cm for a 1.5 m long stainless steel pipeline.We suggest that the simulated results be of some basic and technological interest in development of ultrasonic leak detection of vacuum pipelines.