Magnetic fluids viscous damper is a new type of dampers, whose structure including magnetic fluids, permanent magnet and a non-magnetic container. Inside the non-magnetic container, magnetic fluids supports the permanent magnet to suspense in it and moves as a working element. Under the influence of external oscillatory inertia forces, the movement of the permanent magnet leads the damper to a viscous dissipation of the oscillating system energy. This kind of viscous damper is very suitable for spacecraft under low frequency oscillation. In our experiments, model of magnetic fluids viscous damper and its test circuit were designed. The result of tests indicates that the damper based on magnetic fluids can suppress the low frequency oscillation.