For research the effect of ferrofluids types and sealing conditions on the sealing effective,Fe3O4 used as magnetic particles,the chain PFPE-oil used as base liquid,and a series of ferrofluids with different particle concentrations and different molecular weights of base liquid were prepared,and the effects of the type of ferrofluids and operating conditions on the sealing pressure resistance were obtained.The structures and performances of magnetic particles and ferrofluids were characterized.The ferrofluids types and sealing conditions were test on the built sealing test bench.The results show that the prepared magnetic particles have nanometer size,near-spherical morphology,high saturation magnetization,and the ferrofluid has good dispersion stability.With the increase of particle content and molecular weight of base liquid,the sealing pressure increases first and then decreases.When the mass fraction of particles is 30% and the molecular weight of the base liquid is 4 600 g/mol,the withstand value of sealing pressure is the highest.With the increase of spindle speed,the sealing pressure value decreases gradually.With the extension of sealing time,the sealing pressure value decreases first and then becomes stable gradually.