Abstract: The cladding tube is the main component of the nuclear fuel assembly, and as the first protective barrier, its quality is very important for the safe operation of nuclear power plants. After the completion of cladding tubes, a non-destructive testing is required, in which the ultrasonic inspection is a primary method. This paper introduces the ultrasonic flaw testing method and techniques of the zirconium alloy nuclear fuel cladding tubes for pressurized water reactor（PWR）, which used in automatic ultrasonic inspection equipment, and discusses the detector response to the longitudinal and transverse artificial defects of different length, width, depth and angle. Its actual shape and size are measured by metallographic anatomical analysis for some typical defects to confirm the flaw detection results. Consider its quality and cost control, the acceptance rules are proposed for different defects. The application shows that the existing detection method and process can inspect the fine defects about 10μm at different locations of the cladding tube. Due to the influence of the defect type and orientation, the echo amplitude obtained by the detector is not completely true to the actual size and nature of the defects. In order to ensure the quality of the cladding tube, it is necessary to take appropriate and more strict measures to control the different defects in the actual inspection of the tube manufacturing process.