Abstract: Objective The aim is that motion, evaporation and oxygen diffusion characteristics of activating flux particles with different particle sizes in the powder pool coupled activating TIG (PPCA-TIG) arc is researched through numerical simulation. Methods Based on the coupling solution of continuity equation, momentum conservation equation, energy conservation equation, discrete phase Lagrangian equation and component transport equation. The motion trajectory, transient density field distribution and oxygen element diffusion of activating flux particles with different particle sizes in the arc are obtained. Results Results show that there are significant differences in particle motion trajectory and evaporation behavior due to different particle sizes. 1 μm particles are mainly blown out of the arc zone by outer gas due to their smaller size and do not evaporate. The 50 μm and 100 μm particles exhibit two types of motion trajectories, inner and outer. The inner particles evaporate after entering the high-temperature zone, with the 50 μm particles completely evaporating near the tungsten electrode and the 100 μm particles completely evaporating near the base material, the outer particles fall along periphery of arc and pop out after touching base material. At 0.1 mm on the surface of molten pool, after evaporation of the 50 μm activating flux, oxygen element is mainly concentrated on both sides of arc axis, with a maximum mass fraction of 1.97%. The oxygen distribution corresponding to 100 μm activating flux is more uniform, and all are below 1%. Conclusion The particle size of activating flux significantly affects motion trajectory, evaporation position and oxygen element distribution characteristics of particles in arc. Larger particles are more likely to enter the high-temperature zone and contribute to the oxygen element diffusion law, providing a theoretical basis for the rational selection of activating flux in PPCA-TIG.