Abstract: According to a large number of observations that bottom loss increases linearly with the grazing angle under the condition of small grazing angle,the bottom loss gradient F_dB is proposed for single parameter inversion,and F_dB can be fitted out from basic sediment parameters.The average sound intensity described by F_dB is derived with the normal mode approach.Four propagation regions are divided and the appropriate distance for inversion is determined.By using the relationship between distance and signal delay at receiver,the rules of the wave attenuation is obtained.The results of this paper can inverse F_dB from acoustic signal,which lay the foundation for further single parameter inversion research.