This article proposes a novel magnetorheological (MR) damper offering a higher torque-volume ratio, which are typically designed for knee joints of exoskeletons. By combining the advantages of the multi-disc and multi-drum structures, the magnetic field generated by the coil is fully utilized, so that the MR damper can generate a greater torque within a limited volume. Establish magnetic circuit and theoretical model to provide theoretical basis for finite element analysis. The magnetic flux density is obtained by finite element analysis and the geometric parameters of the damper are optimized by response surface optimization to generate the maximum torque-volume ratio. Finally, we found that the damper designed have a higher torque-volume ratio.