Saturated sand in liquefied state exhibits the characteristics of a non-Newtonian fluid, while it is difficult to obtain a stable liquefied state using a conventional dynamic test. A sample mixing plastic sand and the sodium chloride solution of equal density is prepared to obtain a stable state of almost zero effective stress. According to the theory of low Reynolds number flows around a sphere, the test device for flow characteristics of saturated suspended plastic sand is developed based on the particle image velocimetry (PIV) technology. A half sphere on the inner wall of the transparent model box is embedded in the saturated suspended plastic sand, and it can move in a vertical direction. The movement of the particles around the half sphere which recorded by a PIV device indicates the flow characteristics of the plastic sand in a almost zero effective stress state. The apparent viscosity of the plastic sand is obtained by measuring the movement velocity and force applied on the half sphere. The test results show that the saturated suspended plastic sand is a non-Newtonian fluid, and it can be used as an equivalent material of liquefied sand. Same important concepts, including the zero-velocity bounding line, shearing zone, shearing angle and height of the shearing zone, are proposed based on the micro investigation on the pulling ball tests. The shearing angle of the shearing zone increase with the ball’s velocity increasing. The influencing zone in the direction of dragging ball can be described in the height of the shearing zone. The minimum distance between the ball center with the bounding wall of the model box should be larger than six times of the ball diameter. The hole below the moving ball is due to the high apparent viscosity of the saturated suspended plastic sand. The moving velocity of the ball or pipe in the dragging tests should be as low as that satisfying the theory of the low Reynolds number flows.