Abstract: The present invention provides a pneumatic grinder connected to a driving gear or spindle at the tip end of the coupling shaft, in which a bearing is set upon the front portion for anti-eccentric-shaking, improving the concentricity of the grinder, in order to suit higher running speed smoothly and higher gearing accuracy; the coupling mechanism of the tilting head and the main body is simplified into a single component—retaining cover having two counter revolving oriental threads for securing, meanwhile the sizes of said main body and the driving gear are shortcut; the rotor and the shoots on it are formed in a single process in the injection casting simultaneously, in order to improve manufacturing speed and reduce cost.