Rotary magnetorheological (MR) brake is a kind of semi-active damping device which can effectively generate torque and dissipate motion energy, it has a wide application prospect in the field of automobile braking systems due to its characteristics of adjustable torque and fast response speed. A rotary MR brake with multi-fluid flow channels was developed and prototyped. The magnetic flux was guided into the outside axial fluid flow channel by setting a non-magnetic material in the middle of the rotating sleeve which could improve the magnetic circuit structure greatly, the working area where the MR brake producing rheological effect was increased, and the effective damping gap of the brake was increased from two sections to four sections. The working principle and torque mathematical model of rotary MR brake were expounded. The electromagnetic field of MR brake was modeled and the distribution of magnetic flux intensity in different fluid flow channels of MR brake was analyzed by finite element method. The simulation results showed that the torque of the MR brake was 65.39N·m when the input current was 1A. The experimental test system was set up to test the dynamic performance of MR brake. The test results showed that the brake torque can reach 61.4N·m with loading current of 1.8A and rotational speed of 600r/min, the variation trend of the experimental results was basically consistent with that of the simulation results, and the speed change had no effect on the torque of rotary MR brake with multi-fluid flow channels, which was beneficial to broaden the application of MR brake.