Abstract In order to overcome the shortcomings of the traditional sealing for dry Roots pump, we first designed magnetic fluid sealing and calculated its magnetic field distribution. In addition, since the differential pressure formulas sustained by the seal in most literature are inaccurate or incorrect, we precisely deduced and obtained the differential pressure formula of magnetic fluid sealing before we tested the differential pressure sustained by the seal and the influence of rotation speed on vacuum degree in the test platform. The dry Roots pumps using magnetic fluid sealing have been working well for almost four years up to now, which shows that the performance of the magnetic fluid sealing for dry Roots pump is good. We have successfully developed “the dry Roots pump with magnetic fluid sealing” which was accepted as the state patent and authenticated as the achievement in the scientific research in 2000.