The radial runout of the large diameter shaft greatly increases the gap of the magnetic liquid seal,which seriously weakens the pressure resistance of the magnetic liquid seal.In view of the weakening of the pressure resistance of the large diameter and large gap shaft seal,a magnetic liquid sealing structure with a sandwich magnetic circuit was designed.The magnetic field characteristics and sealing performance of the magnetic liquid sealing structure under the sandwich magnetic circuit were studied using numerical simulation method.The magnetic field distribution characteristics of the sealing gap in the sandwich magnetic circuit sealing structure were analyzed.The theoretical pressure resistance value of the classical structure of magnetic liquid sealing and the new structure was compared and analyzed.The results show that the pressure resistance of the new sandwich magnetic circuit is increased by an average of 20% compared with the classical magnetic liquid sealing structure,and a more significant improvement in pressure resistance can be obtained under large gaps.The near surface magnetic field lines through the shaft shows a greater number compared to the classic magnetic fluid sealing structure for the presence of the inner permanent magnet of the sandwich sealing structure.Furthermore,the sandwich sealing structure is observed stronger magnetic gathering ability according to its larger difference in magnetic flux density.