Abstract: The seamless steel tube made by a certain manufacturer has got depressions on its inner surface at the end as occurring after being detected with magnetic particle process. Taking such a tube as the sample,the depression area is analyzed via tests concerning macro-morphology,metallographic structure and hardness,etc. The analysis result reveals how the said depression is developed. It is because that during the detection process,the electric pole surface of the machine gets oxidized,and thus causes poor contact with the tube surface,which results in excessively-high electric resistance in local area,and the tube inner surface is in turn melted,and electric arc occurs to get the surface burnt. Based on the above mentioned facts,relevant suggestions are proposed to prevent occurrence of the defective tube-end depressions during the magnetic particle detection operation.