The invention discloses an internal hexagonal wrench which comprises a wrench head, a rotating column, a center rotating shaft and a handle. The wrench head is arranged at the top end of the rotating column. The handle is arranged at the tail of the rotating column. The center rotating shaft is arranged in the rotating column. A first gear, a second gear and a third gear are arranged on the center rotating shaft. The wrench head comprises first wrench claws, second wrench claws, third wrench claws and a gear rack. The two first wrench claws are arranged oppositely. A work convex head is arranged at the front ends of the first wrench claws, and the rear ends of the first wrench claws are connected with the gear rack. The gear rack penetrates the rotating column and is engaged with the first gear on the center rotating shaft. The structures of the second wrench claws and the structures of the third wrench claws are the same as the structures of the first wrench claws. The work convex head of the first wrench claws, the second wrench claws and the third wrench claws forms a circle shape. The internal hexagonal wrench is of a mechanical structure and is low-carbon and environmentally-friendly. During use, only a rotating wheel needs to be rotated, an opening of the wrench head is adjusted, the handle is rotated, and demounting and mounting work on an internal hexagonal bolt can be achieved.