In this paper, we analyze the principle of speckle-rotation decorrelation, including the factors that influence the speckle-rotation decorrelation angle. We infer that this angle is mainly affected by the degree of speckle disorder and the size of the speckle area used in the calculation. To perform experimental tests, we change four parameters of the optical system and observe the corresponding changes in the speckle-rotation decorrelation angle. Specifically, we change the speckle area used in the calculation, change the distance between the scattering medium and the detector, shift the detector horizontally, and replace the scattering medium. The experimental results show that the larger the speckle area and the higher the degree of disorder, the smaller is the speckle-rotation decorrelation angle. In speckle imaging based on the memory effect, these research results can help both related research and applications of speckle-rotation decorrelation that have practical significance.