Brake-by-wire system is a more compact, more efficient brake system using electromechanical actuators instead of conventional hydraulic actuators. Magneto-rheological (MR) fluid is widely used in damping control due to its outstanding controllable properties. In this paper, an MR based Brake-by-wire system with self-energizing and brake energy harvesting capability was proposed and designed. It combined a typical single-disk-type MR brake with a wedge mechanism for self-energizing purpose, and a generator is employed to conduct regenerative braking and harvest brake energy. The MR brake and generator are located at the inner side of the wheel rim and coupled by compact linkage and axle mechanism. According to the torque analysis of the proposed MR brake, the brake torque was significantly amplified, which means MR fluid can be applied in automotive Brake-by-Wire system with less power consumption. Meanwhile, about 46W output power of the generator can be achieved when braking at an initial vehicle speed of 50km/h. Using a DC/DC convertor, the output power can be used to power the MR brake control circuit or other in-vehicle electronic devices, or charge the on-board low-voltage battery. Simulation results are given according to the proposed design.