With the fierce competition of high-end chips, Y₂O₃ coating is an important component of plasma etching cavity, corresponding research gradually becomes a research hotspot. Y₂O₃ coating was prepared on aluminum alloy surface by suspension plasma spraying (SPS). The effects of different process parameters on the phase composition, mechanical properties, microstructure, and dielectric strength of the coating were studied. The effect of microscopic porosity of Y₂O₃ coating on etching rate was analyzed after etching in CF₄/Ar/O₂ mixture for 30, 60 and 120 min, respectively. The microhardness, the porosity, the bonding strength, and the dielectric strength of Y₂O₃ coating prepared by the optimal process 1 (spraying distance 80 mm, liquid feed rate 35 mL/min, atomizing gas flow rate 15 L/min, horizontal gun moving speed 700 mm/s, vertical moving step 1 mm/step) is (3.78±0.36) GPa, (2.35±0.24)%, (36.0±3.6) MPa, and (29.74±2.01) kV/mm, respectively. In the mixed plasma gas composed of CF₄/Ar/O₂, the Y₂O₃ coating undergoes physical and chemical reactions, while Ar⁺ strongly shocks and bombards the coating to break the chemical bond on the surface. CF₂* and F* make Y₂O₃ continuously etched to form YF₃ attaching to the coating surface. At the same time, the physical impact of Ar⁺ constantly acts on the surface of the coating, removing the YF₃ layer, and a small amount of residual YF₃ on the surface of the coating is oxidized and finally forms YOF, resulting in a coating etching rate as low as (11.48±5.21) nm/min. Y₂O₃ coating with high density, low porosity and high uniformity can effectively improve the resistance of parts to plasma etching, which is of great significance in semiconductor industry.