A thermal-chemical polishing device and method for polishing a diamond film of a workpiece, the device includes a horizontally displaced first rotatable high rpm shaft and a vertically displaced second rotatable high rpm shaft that are perpendicular. The first shaft is made of a material from transition metals or rare-earth elements which undergo a chemical reaction with the diamond film at high temperature. The circumferential surface of the first shaft has a predefined heating region. The second shaft moves axially towards the first shaft to allow the diamond film to make contact with the heating region of the first shaft. A heating unit is provided to heat up the heating region to create a chemical reaction for thermal-chemical polishing to perform while the diamond film is in contact with the heating region. The device of the present invention increases the rate of polishing and also decreases cost.