Ferrofluid is prepared with the chemical method in order to seal the ship stern shaft. Three types of ferrofluid are obtained. Their magnetic particles all are Fe3O4, but their base solutions are separately water, oil and fluorine ether oil. Experimental results show that the value of saturated magnetic intensity of oil based ferrofluid is higher than the others, and its seal performance is better. Viscosity and density of fluorine ether oil based ferrofluid are the highest. Under the effect of the additional magnetic field, the pressure drops of water or oil sealed by water based ferrofluid are all lower, but the pressure drop of water sealed by oil based ferrofluid is close to an ideal value. Therefore, it has practical value that oil based ferrofluid is used as sealing liquid of ship stern shaft.