Abstract: Due to high temperature operating environment, the main steam pipeline of large boilers cannot achieve on-line detection by conventional testing methods. An on-line detection method was provided based on acoustic emission technology and the acoustic emission sensor was adopted to connect the waveguide rod, an acoustic emission detection experimental system was built for the main steam pipeline of high-temperature boilers. In addition, the lead-cut method was used to simulate the sound source signal when the pipeline cracks, and the sensitivity test, signal attenuation test, sound velocity measurement and positioning accuracy analysis at different temperatures were carried out, which verified the feasibility of using acoustic emission detection technology to conduct on-line detection of the main steam pipeline in high-temperature boilers, and also provided a direction for the future development of acoustic emission technology in the defect detection of high-temperature pressure pipelines.