<p>Knee joint prosthesis is a common metal implant in medical fields. However, the complex surface curvature expression often impedes its further precision processing. This paper describes the application of a magnetic abrasive finishing (MAF) process to yield a fine finish on a complex curved surface. The spherical atomized bonded-type magnetic abrasive particles (MAPs) were prepared by a two-stage atomization method. Different groove depths and scratch densities on the knee prosthesis surface were found after polishing. The magnetic induction intensity and distribution were simulated with the aid of Ansys Electronics Desktop. It was found that the magnetic induction intensity was affected by the curvature. The distribution of magnetic induction intensity tended to be elliptical with the increase of curvature. The results indicated that the deformation involved in the surface morphology was mainly caused by the curvatures. A theoretical force model was developed to predict the force in the MAF process, which has taken the curvature of the workpiece, working gap, abrasives size, MAP distribution, and rotation speed into account. The single-factor experiment showed that the surface curvature of knee joint prosthesis can affect the processing morphology of the spherical diamond MAPs. The larger the curvature, the worse the surface morphology of the workpiece. The trend of theoretical force and the experimental force were consistent; the modelled force agrees well with the measured. This model enabled an in-depth understanding of the mechanical force analysis of spherical magnetic abrasive on the curved surface involved in MAF processing and the effect of the curvatures of the workpiece on its material removal.</p>