Abstract: In this paper, X-ray method is used to test the residual stress of 6061-T6 aluminum alloy welded joints. In order to explore a reasonable stress measurement process, X-ray stress test is performed on the pre-stressed equal-strength beam. The diameter of the aperture and the oscillation angle are successively increased during the test. The full width at half maximum of the diffraction profile is used to characterize the microscopic strain of the diffracted grain group. The change in the uniformity of the microscopic strain of the diffracted grain group is analyzed when the aperture diameter and oscillation angle increase, as wll as performing orientation imaging analysis to compare the grain selection between two stress test scheme in different intervals of preferred orientation of the grains. The results show that the stress test accuracy is related to the strength of the preferred orientation of the grains. In the spatial range where the preferred orientation of the grains is strong, when oscillation angle greater than 1° is used, the adjacent sub-crystals near the small-angle grain boundary can participate in the diffraction, so that the microscopic strain of the diffracted crystal grain group tends to be uniform, so the X-ray stress measurement accuracy is higher, and when the aperture is added in the range of d = 2 ~ 4 mm, the increase of diameter d can increase the number of diffracted grains, but has little effect on the microscopic strain uniformity of the diffracted grain group and the accuracy of stress testing.