Abstract: In the long-term operation of nuclear power plants, ensuring the integrity of the plastic-lined pipe structure of SEK system is crucial for guaranteeing the safety of the entire unit. This study adopted a multimodal fusion detection technology, combining piezoelectric ceramic low-frequency ultrasonic guided wave detection and ultrasonic phased array detection technology, to detect and evaluate the corrosion condition of the carbon steel plastic-lined pipe base, thereby indirectly assessing the basic state of the pipe plastic-lined. In the actual case of a certain nuclear power plant, the corrosion area of the carbon steel pipeline was first determined through the low-frequency ultrasonic guided wave detection of piezoelectric ceramics. Then, the ultrasonic phased array technology was used to detect this area. Next, the basic state of the pipeline matrix and the plastic lining was judged through the C-scan of the ultrasonic phased array and the minimum wall thickness of the area. Finally, the carbon steel pipeline was evaluated in accordance with relevant standards. The application of this technology proved its effectiveness in detecting the corrosion of plastic-lined pipes, providing strong support for the safe service of plastic-lined pipes in nuclear power plants.