Abstract: The stress and damage state of drill pipe in oilfield are detected by multi-channel magnetic memory tester. In order to overcome the disadvantage that gradient from single direction is easy to cause stress concentration region of the same direction as with the testing undetected, this paper proposed a method that combined the gradients of the testing direction and its vertical direction when one aimed to work out the gradient of the tangential component of multi-channel magnetic memory signal. It is proved that this method is better than gradient only from testing direction by the comparison of two methods in multi channel drill pipe magnetic memory testing signals. The method proposed in this paper is of great significance to promote the application of magnetic memory testing technology in the testing of drill pipe and reduce the accident of drill pipe.