Abstract: The metal cutting tools are widely employed in machinery manufacturing industry, and the cutting angle of the tools is intricate and volatile owing to the difference of workpiece and the production conditions. But to date there are scarcely any general formulas used to express the regularity of variation for the cutting angle of different cutting tools. In this paper some general formulas of cutting angle are derived in consideration of the direction of cutting speed and the direction of cutting edge and surface normal of fools-By means of these formulas the cutting angle of any complicated tools can be calculated with convenience.