Abstract According to field measurements, the basic character of the particle size distributions obtained from the landslide accumulations is fractal. The collapse of the granular columns with fractal particle size distribution (FPSD) is performed numerically and experimentally to form dry granular flows and the mechanism of how FPSD affects the particle movements is then investigated. Numerical and experimental analyses show that particle flow mobility increases as the fractal dimension increases. Several linear relationships exist between the fractal dimension and flow mobility parameters. By analyzing the kinetics of granular flows, it is found that a large number of small‐sized particles will form a boundary layer where the particle shearing and velocities are remarkably increased and will thus have a lubricant effect on the flow mobility. Moreover, the number of particle collisions increases, and small‐sized particles are more likely to obtain higher spreading velocities via the greater contribution of particle interactions.