Nitrogen/Oxygen　(N2/O2)　mixtures　are　with　good　insulating　properties　and　economic　benefits,　which　are　widely　used　in　gas　insulation　for　electric　power　equipment.　The　effective　ionization　coefficient　as　well　as　the　breakdown　voltage　of　N2/O2　mixture　is　related　to　the　O2　component　ratio.　In　this　paper,　the　breakdown　voltages　of　N2/O2　mixtures　at　high　pressures　in　non-uniform　electric　fields　are　investigated.　The　applicability　of　Paschen＇s　law　in　N2/O2　mixtures　insulation　under　non-uniform　electric　fields　is　analyzed.　An　empirical　formula　for　the　breakdown　voltages　of　N2/O2　mixtures　is　presented.　The　effect　of　the　O2　component　ratio　on　the　breakdown　characteristics　at　high　pressures　is　also　analyzed.　When　the　electric　field　non-uniformity　is　high,　the　enhancement　effect　by　the　O2　component　ratio　on　breakdown　voltage　is　more　significant.　The　breakdown　voltage　fluctuation　is　related　to　the　O2　component　ratio　and　the　non-uniformity　of　electric　field.　©　2024　IEEE.