This paper described the constitutive characteristics of magnetorheological(MR) fluids using a generalized bi-viscosity model and the principle of MR fluids stepless speed transmission torque and output rotational speed been under the control of the out magnetic field. Taken MR fluids MRF 336AG for example, the relations between magnetic field and yield stress, torque, output rotation speed are researched. The numerical results show that MR fluids stepless speed transmission torque and the output rotation...