The use of a band-aid is not recommended when the nail cap is cut in half by a knife, and you should go to the hospital to have the wound cleaned and stitched up. Wrapping the wound with a band-aid after the nail cap has been cut in half by a knife will not ensure that the wound is dry, clean and protected, and may even worsen the condition by making the wound infected. Should go to the hospital, with iodophor of hydrogen peroxide and other wounds for thorough debridement after removing the excess nail, with iodophor oil gauze wrapped wounds, at the same time under the guidance of the doctor to change the medicine on a regular basis, if the wound is deeper or the knife cuts rust, if necessary, but also need to be added to the tetanus vaccine. After treatment, antibiotics such as amoxicillin and cefaclor can be taken to prevent infection. During the healing process of the wound, you need to avoid water and ensure that it is a dry and clean environment. If the wound becomes infected, seek medical attention immediately to avoid aggravation.