This paper studies effects of shapes on suction performance of a drag head for a trailing suction dredge through investigations on pressure distribution at a bed under a model drag head. Four model drag heads are circular, rectangular, square and the California type. These drag heads heve almost the same velues of the suction area ratio (the area of the suction mouth/that of a suction pipe).
　Flow rate, clearance between a drag head and a bed, and trailing rate are varied at three stages in experiments, resectively.
　In case of a stationary state, the circular drag head shows higher pressure gradient in the vicinity of the circum ference of it, but the California type gives a wider pressure affected region outside the drag head.
　When a drag is trailed experiments show that variation in the pump flow rate and the clearance bring siginficant influence on the absolute values of the pressure at the bed under a drag head, but do not affect greatly the width of the region surroubded by the pressure contour outside the drag head.
　These investigations lead to the conclusion that the California type and the square drag have better performance than others do.