Abstract: In order to analyze the leakage reason of boiler′s water wall, by means of the macro-observation, metallographic, electronic microscope, energy spectrum, and heat erosion analysis, we get the results: blocks of ulcerate corrosion on interior surface of the pipeline, and black lines of micro-cracks in the interior of ulcer, caustic elements such as calcium, aluminum and sulphur in the media. The conclusion is : the leakage source of water wall in 2008t/h boiler is hydrogen damage, in close relation to hypo-pH value of boilwater and excessive high temperature of pipeline surface. Together with analyzing hydrogen damage peculiarity in water wall, we discuss the theorem of hydrogen damage and provide the characteristic of hydrogen damage.