In satellite remote sensing, the relationship between bidirectional reflectance and optical depth is the foundation of the retrieval of the aerosols' optical depth. According to asymptotic integral theory, a new approach to dealing with bidirectional reflectance of atmospheric without artificial stratification in the single-scattering approximation. The results show that the accuracy of analytical solution obtained by the new method is high. We formulate the analytical bidirectional reflectance with the vertical continuity of the inherent optical properties. Moreover, analytical solution is relatively easy to explain some of most import features for radiative transfer process.