Abstract: There often occurs leakage point in large U-tube heat exchanger during its operation. In order to locate the small leakage point accurately, positive pressure helium absorption method is used to detect the leakage. There exist the problem of background helium pollution for the open type of heat exchanger. The method of rubber plug combination with plastic film is developed to carry out helium leak detection on the tube bundle and expansion weld of U-tube heat exchanger respectively. This method can accurately locate the leaking heat transfer tube and shorten the inspection cycle of helium leak detection.