Abstract: Based on the analyses of sound absorption mechanism of particles, the sound attenuation in suspended particulate matter seawater of real sea area is calculated and analyzed according to sea survey data of South Yellow Sea and Laizhou Bay. The results shown that, in the frequency range of sonar working, the sound wave attenuation produced by viscous absorption of suspended particulate matter can not be neglected comparing to the sound wave attenuation in clear seawater. It is know from calculation that scattering absorption of suspended particulate matter can be neglected in the frequency range of sonar working. Taking the partical radius as 2.5 μm, it can be obtained from calculation that the viscous attenuation coefficient will be higher than the attenuation coefficient of the clear seawater when the concentration of the particles is higher than 0.1 kg/m³ for the sediment-class suspended particulate matter and the concentration of the particles is higher than 1 kg/m³ for the organic class suspended particulate matter in the frequency range lower than several kHz. So condition that the concentration of the particles is higher than 0.1 kg/m³ for the sediment-class suspended particulate matterand and higher than 1 kg/m³ for the organic class suspended particulate matter can be seen as a conservative criterion whether the existence and effect of the suspended particulate matter should be considered in the problem of seawater sound attenuation or not. The condition can also be considered as the basic requirment of acoustical turbid for suspended particulate matter seawater.