The backward scattering ratio is not only an important parameter of detecting seawater backward scattering signal based on airborne lidar, but also a very important optical property of oceanic suspended particles. Based on Mie scattering theory and scattering phase function, it puts forward a formula to calculate the backward scattering ratio. According to Mie scattering theory, the scattering phase function characteristics of alga particles and suspended sands are analyzed, and their backward scattering ratios are obtained too. In addition, the relationship between backward scattering ratio and particle radius and lidar wavelength is discussed in detail. From the simulation results, it can be found that, in the condition of the constant lidar wavelength, the backward scattering ratio of the alga particle increases with the increase of alga particle radius, while the backward scattering ratio of the suspended sand decreases with the increase of suspended sand radius. At the same time, in the condition of the constant particle radius, the two main suspended particles' backward scattering ratios increase with the increase of the lidar wavelength.