Nanometer-(70?80 nm) and micrometer-sized (500?600 nm) rare-earth (RE) oxides (La₂O₃, Y₂0₃) were separately mixed with tungsten powder by a mechanical alloying method. Afterwards, the W-1.5La₂O₃-0.1Y₂O₃-0.1ZrO₂ (wt%) was prepared by cold isostatic pressing, medium-frequency induction sintering, rotary forging, and drawing. Then we performed tungsten argon arc welding (TIG) under the same welding current for 0.5, 1, and 2 h on the cathode samples containing, separately, nanometer- and micrometer-sized RE oxides. Results show that the sample with nanometer-sized RE oxides exhibits higher working stability during the welding process, and the burning loss is decreased by nearly 85.4%. Moreover, with prolonging the working time, the aggregation degree of RE oxides in different regions of the tip significantly increases. Combined with the temperature simulation by COMSOL Multiphysics, we found that the diffusion activation energy of the second phase is decreased by nearly 34%. This is because the finer second phase effectively controls the evolution of the tungsten matrix structure, thus preserving many grain boundaries as channels and promoting the diffusion of active substances.