In order to study the influence of different lumpiness on the disintegration characteristics of mudstone , a self-designed test device was used to simulate the actual environment of rainfall in the natural world. The mudstone in the Weinan area of Jiangxi Province was made into 80-70 mm, 70-60 mm, 60-50 mm and 50-40 mm, the samples of different lumpiness were tested in the laboratory disintegration under the action of dry and wet cycles. The results show that, in the curve of the percentage of each particle group, there is a significant peak in the curve under different cycles. The curve basically shows increasing to the peak first, then decreasing. And with the cycle numbers increasing, the peak gradually moves toward the direction in which the particle diameter decreases. Before the peak, as the cycle numbers increases, the position of the curve gradually moves downward; and after the peak, as the cycle numbers increases, the position of the curve gradually moves upward. With the increase of the cycle numbers, the gap between the percentage curves of each group gradually decreased, and the curve under the last four dry and wet cycles was very close, indicating that the disintegration of mudstone gradually stable. The relationship between the cumulative specific surface energy and cycle numbers in the rock disintegration process is analyzed. With the increase of cycle numbers, the cumulative specific surface energy of each sample increases rapidly when the number of cycles is small, and after the second cycles the growth rate gradually slowed down and finally stabilized. As the lumpiness increases gradually, the cumulative surface energy of the sample gradually decreases. Based on the principle of least squares method, the relationship between the cumulative new surface energy and the cycle numbers is obtained, and the correctness of the calculation model is verified.