Abstract: The coral mud is the calcareous ooze composed of fine-grained coral debris, which is distributed in the form of sandwich by particle sorting. During the formation process of an entire filling site, the sedimentary characteristics of the coral mud will have influences on the foundation stability after the filling. Therefore, from the sedimentary characteristics at the initial stage for the stability of the foundation, the effect of the initial concentration on the surface velocity of coral mud turbid surface is explored. The size of flocculation is observed by using the scanning electron microscope (SEM). The theoretical sedimentation velocity of the turbid surface at the constant velocity sedimentation stage is deduced according to the Stokes formula. Through the sedimentation tests on the coral mud, marine sedimentary soil with similar particle composition and Wuhu silty clay with the similar plastic index, the sedimentary characteristics of the three sediments are compared and analyzed. The results show that the height of turbid surface decreases with the decrease of the initial concentration during the sedimentary processes of three kinds of soil. At the constant velocity sedimentation stage, the settling velocity of turbid surface decreases with the increasing initial concentration, and the change is gradually mitigated and stabilized. The difference is that the settling velocity of coral muddy surface appears at the earliest time, and its sedimentation rate is much higher than that of the other two kinds of soil. The time at the constant velocity sedimentation stage is only 1/3 of that of the other two kinds of soil, and the initial concentration has the most obvious effect on the constant velocity sedimentation time of coral mud. Finally, the relationship between the initial concentration and the turbid surface is obtained. It is of a practical significance for the construction of dredge fill and safety and stability of foundation in South China Sea.