Long-time partial discharge (PD) is regarded as one of the main reasons for the insulation failure of high-voltage cables. In this work, we report on the application of atmospheric pressure plasma to deposit siloxane film on copper to avoid PDs. The dielectric barrier discharge (DBD) plasma is driven by AC power supply, with tetraethoxysilane (TEOS), argon, and oxygen mixture as the source gas. The effect of oxygen gas flow rate on the thin film surface morphology, chemical composition, and electrical properties is studied systematically. Our results show that the stability of the plasma deteriorated, when the oxygen flow rate exceeded 10 sccm. The addition of oxygen in the source gas induced a high oxidation level of deposited thin film. The chemical composition of thin film was in the form of SiOx (x = 1.9) with 10 sccm oxygen compared to SiOx (x = 1.2), when deposited in the absence of oxygen. Additionally, the optimal thin film with good stability was obtained with the surface resistivity 1.1 × 1011 Ω, when deposited in the absence of oxygen. The corresponding relative permittivity of the deposited thin film is 2.9. The simulation results demonstrated that the electric field distortion was weaken after the film deposition, which reduced the probability of PD to occur.