In terms of Airborne laser bathymetry backscattering lider equation ,the backscattering envelop is analyzed in the field of frequency . The frequency included in backscatter envelop would broad 236MHz and 220MHz when the attenuation coefficient of sea water changes from 0. 2/ m to 0. 9/ m and the albedo of the sea water changes from 0.1 to 0. 9 respectively. The altitude of the plane and the optical receiver field of view have little effect on the frequency of backscattering signals. When the sensitivity of the detecting system is 1. 56 ×10 - 10W , the frequency width of backscattering envelop is 0 < f < 5. 6 ×108Hz ,under the typical experimental parameters.