Surface treatment of Al

2

O

3

-filled epoxy resin（Al

2

O

3

-ER） by atmospheric pressure plasma can effectively improve its surface insulating properties. In order to further improve the discharge uniformity and treatment effect

the effect of O

2

on the film deposition of atmospheric pressure plasma jet was studied. In the experiments

the carrier gas was argon（Ar） and the precursor was tetraethyl orthosilicate（TEOS）. The concentration of Ar/TEOS mixture gas was kept constant in the jet tube and the substrate heating tem

perature was set to 100 ℃. Deposition time was 3 minutes. Effect of the oxygen concentration on the film deposition was investigated. The experimental results show that the absorption peaks of Si—O—Si and Si—OH increase and the chemical concentrations of silicon and oxygen spices increase after a proper amount of oxygen is injected into Ar/TEOS mixture

and the reasons are that the Penning ionization in Ar/O

2

mixture is enhanced and the TEOS is sufficiently dissociated. The observation of surface topography shows that nano-particles fused with the film after the deposition without oxygen appear on the Al

2

O

3

-ER surface. When O

2

concentration is 0.8%

the Al

2

O

3

-ER surface presents a flocculent structure. Furthermore

surface potential distribution tests show that the peak potential will decrease by about 50% after 1.6% O

2

addition

meanwhile

the average flashover voltages will increase by more than 34.2%. The experimental results provide references for further optimization of film deposition conditions and the study on the surface flashover improvement of Al

2

O

3

-ER sample.