Abstract: The heating surface tube of the cyclone separator in the power plant leaked twice successively. In order to prevent the recurrence of similar leakage accidents, the leakage reason was explored. The macroscopic inspection on leaking tube surface was conducted, and its mechanical properties at the room temperature were tested. The techniques, including the Brinell hardness testing, metallographic inspection, scanning electron microscope coupled with energy dispersive spectrometer analysis were also applied. The results show that when the urea solution dripped on the heating surface tube, the corrosion reaction occurred between the decomposed product at the high temperature and the metal of the heating surface tube of the cyclone separator, thinning the effective wall thickness of the heating surface tube. In this way, the leakage accidents occurred due to the unbearable pressure of the internal media. Finally, combined with the operation status of the heating surface tube and the cause of leakage, relevant suggestions such as strengthening the normal inspection, optimizing the atomizing air pressure, and installing peripheral tube surface protection materials are put forward.