Red clay has a special aggregate structure due to the existence of free iron oxide in the soil. It is recommended to add dispersants in various specifications for particle analysis of red clay by densitometry. In order to better evaluate the dispersion effect of soil samples, fractal theory is used to describe the particle size characteristics of soil particles with fractal dimension. The results show that the fractal dimension value is larger and the soil particle aggregate is more dispersed when sodium hexametaphosphate solution is used as dispersant. It can be seen that the dispersion effects of different dispersants on the red clay used in the experiment are quite different, and the actual particle size distribution of red clay can be better obtained by adding appropriate dispersants. The experimental results are of great meaning for further understanding and mastering the engineering properties of red clay.