The utility model relates to the field of medical auxiliary instruments, and discloses an acupuncture pen for positioning a subcutaneous mark for radiotherapy. The acupuncture pen comprises a pen tube, a pen core, and a needle. The lower part of the cavity of the pen tube is provided with an upper partitioning part and a lower partitioning part. The center of the upper partitioning part is provided with a through hole which can enable the pen core to pass in a sliding manner, and the center of the lower partitioning part is provided with a through hole which can enable the needle to pass in a sliding manner. The lower end of the pen core is provided with a blocking disc, and a spring is disposed between the blocking disc and the lower partitioning part. The center of the lower surface of the blocking disc is provided with the needle. The interior of the cavity of the pen tube lower than the lower portioning part is provided with dye water absorption cotton. The needle passes through the dye water absorption cotton, and then the tip of the needle can be exposed out from or draw back to the pen tube. Dye water is gentian violet liquid medicine. A side surface of the needle body is provided with a trench which extends along the length direction of the needle. The beneficial effects of the utility model are that the acupuncture pen changes a body surface mark into a subcutaneous acupuncture mark, and changes common dye into gentian violet liquid medicine; the subcutaneous acupuncture mark is marked under the skin, cannot fall off and be lost because of friction, and can be maintained for a long time; the subcutaneous acupuncture depth can be automatically limited; the subcutaneous mark is clear; the acupuncture pen employs the gentian violet liquid medicine, and cannot cause infection, so the acupuncture pen is safe for application.