Introduction: Civil engineering personnel often use the coarse-grain particle distribution fractal dimension and coarse material contour fractal dimension as the basis for the quantitative study of soil-rock mixture, to explain the mechanical properties of the soil-rock mixture, and use these parameters as the soil-rock mixture. The basis of the project classification. The current technicians use manual screening experiments to calculate the fractal dimension of the particle size. The study on the microstructure of the soil-rock mixture is labor intensive and inconvenient to operate, which greatly restricts the study of the microstructure of the soil-rock mixture. A method for measuring the fractal dimension of soil-rock mixture using digital image processing technology is proposed. The experimental verification results show that the method reduces the labor intensity of manual testing by engineers and technicians, and is practical and effective.