Optical emission spectrum of discharges under different background air pressure was obtained using an intensified charge-coupled device (ICCD) and a grating spectrometer. Besides, spectral lines of N2+ (B2∑u+→ X2∑u+, 0-0, λ=391.4nm), N2+ (B2∑u+ → X2 ∑u+, 0-1, λ=427.8nm), He (33S1→23P1,λ=706.5nm) and O (35P→35S,λ=777.4nm) were selected to study their time variation. The results showed that under 4.0 Pa background air pressure, He (33S1→23P1, λ=706.5nm) appears earliest, while in the case of under 20 Pa background air pressure, all lines almost show up at the same time. Besides, He (33S1→23P1, λ= 706.5nm) dies out immediately while other lines keep certain intensities after the current pulse. This is attributed to the concentration of metastables and the occurrence probability of Penning ionization. Because of the metastables, Penning ionization is processing and spectral lines of N2+ and O can be detected even after the extinction of discharge.
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