Abstract: During the X-ray residual stress detection of 5A06 aluminum alloy plate, it was found that the aluminum layer of its surface would interfere with the diffraction pattern, especially the diffraction peak position. In order to obtain independent package aluminum layer and substrate diffraction peak position, this article firstly selected package aluminum with its layer thickness being greater than the ray transmission depth of 5A06 aluminum alloy plate, and then removed the package aluminum layer of 5A06 aluminum alloy as experimental object, and pure aluminum sheet for reference. By doing so, an experimental test on diffraction peak position was carried out by the above-mentioned three. The experimental results showed that the difference of the number of detector channels was about 90, which was the same as that of pure aluminum. From the result, the author analyzed the relationship between residual stress, interference series, equipment operation factors and the diffraction peak position deviation based on Bragg diffraction law. In this paper, the crystal surface of diffraction is enumerated, and the relation between the diffractive crystal surface exponent and the diffraction peak deviation is given. By analysis, the cause of the difference between the two diffraction peaks was due to the difference of lattice constants.