This study explores the size-effect of silicon-based acoustic micropillar chip for the trapping of particle. Experiments and simulations were carried out in the case of micropillars with different height-diameter ratios. The results show that within a certain range, with the increase of the height-diameter ratio of the micropillars, the particles rotate faster and the particle trajectories are closer to the micropillars, so that trapping ability of the chip is significantly enhanced. At the same time, with the increase of the height-diameter ratio of the micropillar, the acoustic radiation force on the particles increases, resulting in improved trapping under higher streaming velocity. We also characterize the size influence of silicon-micropillar on particle trapping efficiency, which shows great potential in subsequent particle or cell studies, and providing a practical low-cost, low sample consumption and convenient tool for single-cell related studies.