In these decades, the turbulence mixing of micro-ejecta particles and gas has attracted considerable attention because it has great influence on inertial confinement fusion and some technologies of optical detection. It is significantly important for studying the evolution of micro-ejecta by investigating the influence of particle size and the transporting progress. In this paper, we experimentally investigate the micro-ejecta dynamical behaviors when a strong shockwave acts on Sn micro-sphere particles with different sizes of 0.1 μm, 1 μm, 5 μm and 10 μm. A strict experiment is carried out, in which a thin Ta flyer is accelerated by TNT explosion to load the Sn particles, and the velocity variation of ejecta particles transported in air is measured by the displacement interferometer system for any reflector. The results show that the tip-velocity of the micro-ejecta is very sensitive to the initial size of particle, where the larger size results in increased velocity. By analyzing the results of each case in detail, we discover that the formation of micro-ejecta is caused by the interaction between shockwave and the gap structure among several particles, where the larger gap structure induces faster ejecta tip-velocity. To verify this explanation, the effects of particle size on the ejecta tip-velocity is examined by simulating the cases of 5 μm and 10 μm in particle size through three-dimensional smooth particle hydrodynamics method. The simulated tip-velocity results are in good agreement with the corresponding experimental results. However, the scenario is different when the particle size is smaller than 1 μm, where the experimentally measured tip-velocity of 0.1 μm size particle is nearly the same as that of 1 μm size particle. We attribute this to the fact that the gap structure is too small to affect the micro-ejecta progress and the micro-ejecta is mainly caused by the large scale defects accumulated by a huge number of particles. Furthermore, by comparing with the experimentally measured velocity decay, we also estimate the size distribution of ejecta particles by simulating the decelerating processes of different-sized particles with different initial velocities in gas. This paper is helpful in comprehending in depth the micro-ejecta process caused by the shockwave acting on micro particles, and also in designing such experiments accurately.