PURPOSE: To obtain a knife with good cutting quality and high performance by depositing fluid abrasive grains formed by mixing diamond powder with oil on the surface of a base board made of a soft material of resin, metal, etc., pressing a bit against the surface of the base board, and relatively sliding these to carry out polishing.

CONSTITUTION: Fluid abrasive grains 2 which are formed by mixing diamond powder having an average grain diameter of 0.2W6μm with olive oil or light oil are deposited on the surface of a base board 1 made of a soft material of resin, metal, etc. While rotating the base board 1 the surface of which is coated with the fluid abrasive grains 2, a ceramic knife H is pressed against the surface while being kept at a defined angle to polish its bit. In this method, since the fluid abrasive grains 2 polish the ceramic knife H while slightly biting into the surface of the base board 1 made of a soft material, no excessive force is applied to the bit S hardly causing the chipping of the bit S, and the width (t) of the bit S can be made sharp to approx. 0.2W0.5μm, making the title method suitable for the final finishing.