This work proposes an innovative magnetorheological fluid (MR) brake design with a multi-disc structure and adjustable MR fluid working gap to enhance braking efficiency. Simulations of the three-dimensional static magnetic field, varying by electrical current and gap state, were carried out in ANSYS Workbench. Magnetic field distribution across the working gaps was analyzed and brake performance evaluation was complemented by test bench. Results indicate a relatively uniform magnetic vector distribution within the MR fluid working area, suggesting a well-conceived magnetic circuit design. While theoretical and experimental results generally align, discrepancies widen at higher currents. Braking torque surges from 0 A to 2.5 A, and then moderates from 2.5 A to 4.0 A, peaking at 146.4 N·m, which is a 25.80% increase over the non-gap change condition. Achieving a torque-to-volume ratio (TVR) of 48.81 kN·m/m3, the designed brake surpasses traditional MR brakes in compactness and torque adjustability. This design methodology and experimental findings offer valuable insights for advancing MR brake structural research.