Based on the fractal theory,elasticity analysis and marginal yield analysis,this paper studied the fractal model of soil cluster structures under different precious hardwood stands in the central subtropical region of China. It has been proposed that the modelY = aD_w^β1D_d^β2 dry can be used for the analysis of the relations between fractal dimension of soil cluster structure and soil fertility, as well as the effects of soil cluster fractal changes on the soil natures in the forest stands. The results showed that the more the contents of the cluster > 0.25 cm and the water-stable cluster, the less the fractal dimension of soil cluster and the higher the soil fertility were. There existed close relationship between fractal dimension of soil cluster and the contents of soil cluster or water-stable cluster composition in the hardwood stands. There also exited remarkable quantity relationship between fractal dimension of soil clusters and soil fertility under different hardwood stands. Castanopsis kawakamii stand has the greatest advantages in the soil structure stability, soil and water conservation, soil self-fertilization capability in comparison among all the 7 hardwood stands. Obviously the fractal model have provided a new means and a new scale for the description of soil fertility, and at the some time it will lay a solid foundation for the forest soil management of the different precious tree stands in the central subtropical region of China.