Abstract: The cause of burst of 20G steel boiler water wall tube in a power plant was analyzed by macro analysis,chemical composition testing, fracture analysis, hardness testing, mechanical performance testing using optical microscope,scanning electron microscope, EDS and direct reading spectrometer. The results show that the water wall tube undergoes short-time overtemperature, the highest temperature is above 854℃, which leads to the burst of the boiler water wall tube eventually.