Abstract: In order to solve the problem of large shaft diameter sealing in engineering application, a large gap magnetic fluid sealing device with split structure is designed in this article. The magnetic field simulation calculation of the designed sealing structure was carried out by using the finite element method, and the magnetic induction intensity distribution of the sealing structure under different sealing clearance was obtained, and the optimal sealing clearance was determined to be 0.5 mm. Based on the optimized sealing structure, a magnetic fluid seal test bench was built, and two kinds of magnetic fluids MFA and MFB with similar saturation magnetization and different viscosity were used to carry out the static sealing, dynamic sealing and sealing lifetime test. The test results show that the split sealing device has good sealing performance. Under the static sealing condition, the critical sealing pressures of MFA and MFB are reduced by 7.1% and 6.9% respectively compared with the simulation results, which are within the acceptable range; Under the condition of dynamic sealing, the critical sealing pressures of MFA and MFB both decrease with the increase of rotating speed, and the decrease of MFB with higher viscosity is smaller; The sealing lifetime of magnetic fluid seal decreases with the increase of rotating speed. Due to the friction heat effect, the sealing lifetime of MFB with higher viscosity is lower than that of MFA.