Based on the plasma-modified model and photoionization optimization model, this article constructs a low temperature and subatmospheric pressure air surface dielectric barrier discharge (SDBD) model with 37 plasma chemical reactions composed of 18 particles. Through the model, the characteristics of air SDBD at low temperature and subatmospheric pressure are studied. Under a dc voltage of 12 kV, with the propagation of the streamer, the parameters, such as electron density, $\text{N}_{2}^{+}$ density, N2(C) density, $\text{O}_{2}^{-}$ density, electron temperature, space charge density, electric field, and photoionization rate, show a downward trend at an altitude of 11 000 m but always maintain N2(C) density > electron density > $\text{N}_{2}^{+}$ density > $\text{O}_{2}^{-}$ density. In addition, the propagation velocity of streamer along the surface is positively correlated with altitude. Electron, $\text{N}_{2}^{+}$ , N2(C), and $\text{O}_{2}^{-}$ density are negatively correlated with altitude. Photoionization rate is positively correlated with the altitude in the streamer development stage. In the streamer propagation stage, except for the sudden drop at the altitude of 11 000 m, it is basically consistent at other altitudes. [ABSTRACT FROM AUTHOR]