Abstract: Taking cold-pulled thin walled tubes of 6061 aluminum alloy and cold-drawn thin walled tubes of 0Cr21Ni6Mn9N stainless steel as example, through the application of visual inspection, fluorescent penetrating inspection and metallurgical analysis, the possible causes of anomalous signals in eddy current testing of thin walled tubes were studied. In this paper, the main cause of anomalous signals was found to be the inner surface cracks in aluminum alloy tube, and was found to be the inhomogeneous deformation of wall in 0Cr21Ni6Mn9N stainless steel tubes. The study also provides references for the signal judge in eddy current testing of other similar tubes.