The dispersion status of Guiyang red clay in different media environment was accurately tested in the present research. In the light of the effect of Guiyang red clay’s special microstructure on particle size distribution, particle size analysis test was carried out using mechanical grinding method, ultrasonic method, and chemical dispersion method, respectively, to study the particle size distribution law. Results unveil that the dispersion of soil particles treated with chemical reagent is better than that with mechanical grinding or ultrasonic wave. Five types of chemical reagents were further used for particle dispersion, among which sodium hexametaphosphate ((NaPO₃)₆), as a strongly alkaline and weakly acid salt, has the optimum dispersion effect. Moreover, concentration, temperature, and test dose were selected as influential factors to obtain the most favorable dispersion conditions for Guiyang red clay: (NaPO₃)₆ solution with a concentration of 2% and dose of 10-15 mL at a temperature around 40 ℃. On such basis, the dispersion mechanism of Guiyang red clay was expounded: cemented agglomerations, a particular spatial structure, were formed among the micro-structural cells of Guiyang red clay via free iron oxide. Free iron oxide is of strong activity and is prone to be hydrated under varying environment, thus affecting the fastness of cemented agglomerations, and therefore is a key factor leading to different dispersion effects.