A fractal-based expression for particle size distributions of coal and gangue was presented, and experiments were undertaken to study the impact of the structural parameters of the rotating crushing mechanism on the separation of coal from gangue. The results of the experiments using cylindrical rod drums with different rod-diameters showed that the crushing effect of a cylindrical rod drum with a rod diameter of 22mm was the best; the results of crushing experiments using different types of rod drums showed that the crushing effect of the triangular rod drum proved fruitful. Because of their higher gangue crushing rate, cylindrical rod drums were more suitable for squirrel-cage selectivity-type underground coal and gangue separation equipment. In addition, the particle size distributions of coal and gangue were obtained and the mass ratio equations of gangue separation under different distribution conditions were deduced. The rotating crushing mechanism has been found to be more efficient than other recent patents for the separation of coal from gangue underground.