Abstract: The magnetic flux concentrating performances of a magnetic fluid sealing device with opposite-pole teeth for a large sealing gap were numerically investigated with FEM(finite element method) and compared with those of a traditional magnetic fluid sealing device with single-side pole teeth.The results show that the magnetic fluid sealing device with opposite-pole teeth yields a much better sealing effect than that with single side-pole teeth.Compared with the latter,the difference in maximum magnetic flux density of the former is greatly increased at the middle pole tooth along the sealing gap direction,and the sealing pressure is approximately doubled.Especially,it is helpful to overcome centrifugal forces produced by high speed rotation on magnetic fluid for application in sealing of high speed shaft.