The invention provides a centering mechanism of a button bit sharpening machine and belongs to measuring tools. The centering mechanism mainly comprises a fixed plate (1), a mandrel (3), a sliding sleeve (5), a centering cap (6) and a centering cross (7), and is characterized in that the fixed plate (1) is arranged on a sharpening machine lifting rack by bolts, the mandrel (3) can rotate along with a bushing (16); an oil injection hole (9) is formed in the bushing (16), the sliding sleeve (5) is arranged on the mandrel (3); the centering cap (6) is fixed on the sliding sleeve (5) by a pin (21), and the centering cross (7) is arranged on the centering cap (6) by a nut (13). The centering mechanism can assist in completing precise centering of a drill bit with a grinding wheel vertical center line and a driving disk center line, can realize quick positioning, and can improve the grinding efficiency.