Optical glass is widely used as the most important basic material in optical field. In this paper, four different shape finishing tools are designed for polishing flat K9 glass by using magneto-rheological finishing process. Influences of the finishing tool’s shape on surface roughness are investigated and analyzed under different related parameters such as finishing time, rotational speed of tool and finishing gap. The result shows that the slotted tool could obtain better surface roughness than the non-slotted tool under the same conditions. Through changing the magnetic field intensity, finishing gap, rotational speed of tool and finishing time, an orthogonal experiment is conducted to obtain the optimal finishing process parameters.