A medical drill bit comprises an accommodating slot disposed concavely on a main body of the medical drill bit, a separate board disposed in the accommodating slot to separate the accommodating slot into a first slot and a second slot, and a lid engaging with the separate board and covering the accommodating slot. The lid and the separate board do not rotate with the main body when the main body in rotation. The accommodating uses to fill with cooling liquid which able to be pumped out from the accommodating slot, and fresh cooling liquid is able to inject into the accommodating slot for cooling the drill bit in rotation.
