Objective To optimize the blade design of thrombectomy device through numerical simulation, and to analyze the influence of structural parameters and rotational speed of the blades on the flow field. Methods Firstly, thrombus had been prepared by refrigerating on retention of blood. Then, the critical speed and the critical velocity gradient had been obtained in the flow field while the thrombus was broken under different attacked angle by the water hammer experiment. Finally, numerical simulation of flow field in the rotary cutting thrombectomy device was carried out by using computational fluid dynamics, and the influence of rotational speed and helix angle of the blades on the flow field were analyzed. Results The critical speed was about 5 m/s and all the velocity gradients were not less than 1 m/s for broken thrombus under different attacked angle. The proportion of the effective velocity which was greater than the critical velocity were positively correlated with the rotational speed of the blade and negatively related to the blade helix angle. Moreover, the velocity gradient in the flow field was positively correlated with the rotational speed of blade. Conclusions In order to optimize the design of thrombectomy device, larger rotational speed of the blade and smaller blade helix angle should be applied on the premise of ensured safety.