Abstract: In this paper, an improved theory about propagation of sound in highly concentrated suspensions is elaborated. The thermal wave and the viscous wave as well as the compressional wave are considered in the multiple scattering process among suspended particles. The compressional wave length is assumed to be much longer than the diameter of suspended particles. The sound field caused by the scattering thermal or viscous waves is analysed rigorously under some reasonable statistic hypotheses. The formulas for calculating the effective density and the effective bulk modulus of suspensions are derived and discussed in the paper.