Abstract: The flocculent structure of slime has a significant impact on its own sedimentation process. In view of the problems in the process of slime water treatment, such as different flocculent structure caused by water flow shear, resulting in poor settlement effect, this paper discusses the effect of mechanical shear on flocculent structure formed by different molecular weight flocculants and the effect of flocculant structure. The influence of mechanical shear on the flocculent structure, the particle size distribution and the transmission ratio of the supernatant were studied by tracking and photographing the floc with PIV particle velocimeter and spectrophotometer. The effect of mechanical shear on the viscosity and molecular chain structure of the flocculant was studied by using rotary viscometer and Scanning Electron Microscope (SEM). The results show that the change of mechanical shear strength affects the particle size, effective density, viscosity and molecular chain structure of flocculent. With the increase of mechanical strength, the transmission ratio, floc size and effective density of the supernatant first increase and then decrease. When the rotating speed is 300～400 r/min, the maximum effective density of floc is 673.14 kg/m3, the proportion of the content with the particle size greater than 0.3 mm is 96%, the transmission ratio of the supernatant reaches 94.8%, resulting in the best sedimentation effect of floc. The increase of mechanical shear strength reduces the viscosity of the agent, makes the molecular chain of the agent break, changes the force between agents, reduces the adsorption performance of the agent, reduces the net catching effect, and affects the effect of the agent. When the rotational speed is 200 r/min, the viscosity of different molecular weight flocculants reaches the maximum value 8.5 mPa·s, which indicates that the molecular chain structure of flocculants is the most complete. This research investigates the mechanism of the effects of mechanical shear strength on the sedimentation process of coal slime floc through changing the mechanical shear strength and promoting the sedimentation process of coal slime floc, which provides a technical support on the process of efficient solid and liquid separation.