Soft rock is a common rock mass in engineering, one of its characteristics is water swelling and disintegration. In this paper, the nonlinear fractal geometry is introduced and the correlation fractal dimension is used to study the characteristics of slate disintegration, based on the laboratory test of water immersion disintegration, the method of quality fractal dimension is used to solve the fractal dimension of the disintegration of slate, and the change of fractal dimension is used to reflect the characteristics of the softening and disintegration of slate when encountering water. The experimental results show that the fractal model can be used to fully understand the development and evolution of rock disintegration process, and to quantitatively link the relationship between rock expansion and disintegration. The conclusion has guiding significance for engineering practice.