Based on Brillouin scattering frequency-shift model of laser transmitting through medium and relative atmospheric data, an atmospheric detection model based on detecting Brillouin scattering signal is established. In this model, Brillouin frequency shift is only correlative to the atmospheric altitude. The continuous distribution state of Brillouin frequency shift of low atmosphere is described in detail. The result shows that atmospheric Brillouin frequency shift is distributed from 1.0～1.3 GHz at the altitude from 0～86 km. This model, presents the data agreeing well with practical data and has good continuity and generality.