The invention relates to a magnetic fluid damping device, which is suitable for damping long objects in spacecrafts and solves the problem of the damping of the long objects in the spacecrafts. The device comprises a non-magnetic shell (2), magnetic liquid (3), a permanent magnet (4), a nut (5), an end cover (6), a bolt (7), a screw (9), a sealing gasket (10) and an O-shaped seal ring (11). The parts are connected in a way that: the permanent magnet (4) is arranged in the non-magnetic shell (2); the end cover (6) with the O-shaped seal ring (11) is fixed to one end of the non-magnetic shell (2) by the bolt (7) and the nut (5); the magnetic liquid (3) is filled into the non-magnetic shell (2) by a threaded hole (8); and the non-magnetic shell (2) is sealed by the screw (9) and the sealing gasket (10). The device is sensitive to inertia force, can perform damping on the vibration with the characteristics of low frequency, small displacement and low accelerated speed, and has long service life and simple assembly method.