The influence of the operating condition against the dredging capacity and the turbidity were investigated in dredging by pump dredger.
　It is clarified that the solid concentration measured by the mud meter varies as dredging thickness and swing speed jointly. The turbidity depends on the ratio of short absorbed soil which is given by the amount of soil excabated by the cutter and that absorbed through the suction pipe. And this value increases hastily with the ratio of short absorbed soil.
　Further the ideal operating condition in which the turbidity is lower than the regulated value is presented. The turbidity around the pump dredger strongly depends on the phisical character and the shape of sea ground.
　It is revealed that the turbidity at arbitrary location of several ten meters far from the cutter doesn't depend on the existence of the pump dredger in the steady dredging in where the thick soft mud layer is not accumulated.