Abstract: In the ultrasonic testing of nuclear zirconium alloy thin-walled tube, the sensitivity of detection of defects generally requires for approximately 5% of wall thickness. Because of the tube wall thickness being less than 1 mm, it is difficult to distinguish between inside and outside wall defect and hence the testing system needs very high detection sensitivity and resolution in order to meet the requirement of automatic testing. This paper focuses on the analysis of the influence of high frequency narrow pulse probe on the detection sensitivity and resolution. Three different parameters of the probe were selected to verify the analysis results, and the method of selecting probe was determined in the detection of small diameter thin-walled zirconium alloy tube.