Abstract: In order to optimize the processing parameters of nanostructured coating prepared by plasma spraying, the change of nanoparticle size during plasma spraying was investigated. Based on the Brook's classical theory about grain growth, a computational model for analyzing the nanoparticles growth of plasma-sprayed nanostructured agglomerated ZrO₂-7% Y₂O₃ powders was established. The effects of the thermal circulation curve and nanoparticle diameter on grain growth were studied. Meanwhile, experiment of plasma spraying using nanostructured agglomerated powders was carried out. The results showed that the nanostructured coating had a bimodal microstructure, which was composed of both fully melted regions and partially melted regions. The partially melted regions were composed of slightly grown-up nanoparticles. The obtained experimental results showed a good agreement with the calculated results, which indicated that the nanoparticles growth theory based on the Brook's theory was correct and reliable. The theory provides theoretical basis for nanoparticles growth of plasma spraying.