Abstract: The formation of thrombus is closely related to the hydrodynamical conditions.Chandler's experiment and further research shows that the cause thrombus formed inthe lower meniscus may be that the fluid particles at relatively high speed strike on thelower meniscus leading to the gathering of platelet and red blood cells(RBC).Thispaper deals with the motion of viscous liquid column with finite length and two freesurfaces in a vertical straight tube under the action of magnetic fields,numericalsolution is obtained by the time-dependent method in a finite difference technipues.The results show that under the action of a proper magnetic field. the axial velocity atthe lower meniscus near the axis will decrease. strike on the lower meniscus will bereduced and then thrombus formation at the lower meniscus can be avoided.Thisresult provides a guide to further experimental research on the mechanism of thrombusformation and medical treatment to thrombus.