Abstract: The failure and leakage of boiler materials in thermal power plants is one of the main reasons for the unplanned shutdown of units, and the causes of material failure and leakage are complex. However, there is relatively little failure leakage due to fin welding. Based on the leakage of vertical water wall of the side wall of the boiler of a 660MW unit of a power plant, this paper tests the failed pipeline by methods such as macroscopic analysis,mechanical analysis and metallographic inspection of metal materials, and analyzes the causes of leakage based on the actual situation on site. The test results found that the leakage of the pipeline was the cracking of the pipe fin,and the crack extended to the water-cooled wall pipeline, resulting in the pipe bursting under high temperature and high pressure. This research and analysis aims to put forward a new analysis idea for the leakage failure of boilers in power stations, and provide a technical basis for reducing the number of non-stop units.