It is a necessary condition to define the relations between acoustic parameters and physical properties, in estimating physical properties of soft mud sediment in sub-bottom near sea bottom surface by acoustic remote sensing on board. In this paper, it is confirmed, by numerical simulations using the theory based on the N-phase suspension model (Tsuchiya et al. 1990), that influences of grain size and volume concentration in suspension are greater than that of dry particle density and compressibility ratio. The frequency dependence, ie. dispersion, of sound velocity ratio when acoustic parameters chosen grain size and volume concentration is also presented. Relations between physical properties and specific acoustic impedance calculated at practical 3 kinds of frequency are explained. Moreover, physical analyzed data by core sampling in Tokyo Bay shows a considerable agreement with our numerical simulations. Therefore, it is possible to estimate with high precision in situ physical properties if both dry particle density and compressibility ratio in these parameters have the usually constant value, respectively.