The working mode and the mechanical model of magnetorheological fluid (MRF) damper are established. The MRF damping system was built by using designed damper, and the MRF damper application in milling chatter control was studied. Theoretical analysis shows that the stiffness and damping of the MRF damper increases with the increase of magnetic field strength, and the amplitude of main vibration system decreases with the increase of the magnetic field strength. Its damping effect will gradually increase with the increase of magnetic field intensity, but not the greater field intensity will be, the better its effect is, while there is an optimal value. As long as choosen suitable field strength, using MRF damping device can control the produced milling chatter phenomenon.