Pulsated Orifice Ejection Method (POEM) is a typical containerless heat transfer and solidification process for preparing micron-sized spherical particles. The heat transfer mechanisms dominated by convection and radiation are crucial for the preparation process, solidification process, and microstructure control. In this paper, a numerical calculation model for particle heat transfer and solidification in a three-dimensional spherical coordinate system was established to investigate the heat transfer and solidification characteristics of micron-sized metal particles prepared by the POEM. The temperature distribution, variation, and solidification process of the particles during the preparation process were calculated and analyzed, and the relationship between grain size and cooling rate for particles with different diameters was discussed. In addition, the influence and contribution of convection and radiation on the surface heat flux density of the particles were simulated and analyzed. This research provides references for optimizing the preparation process and solidification microstructure of micron-sized spherical particles using the POEM.