The invention relates to the technical field of medical dressing, and specifically relates to an external medical dressing for first aid of burns and a preparation method thereof. The medical dressing comprises the following raw materials in parts by weight: 40 to 50 parts of chitosan quaternary ammonium salt, 25 to 35 parts of indigo naturalis powder, 8 to 12 parts of humectant, 3 to 7 parts of bletilla striata extract, 3 to 7 parts of garden burnet extract, and 3 to 7 parts of Japanese eupatorium extract. The provided medical dressing can rapidly stop bleeding, relieve pains, protect wounds, and eliminate scars, at the same time, is capable of inhibiting the growth of bacteria, and can be well attached on the wounds. Moreover, the medical dressing can relieve wound pains, control local infection, maintain the moisture of skins of wounds, protect skins, promote wound healing, and prevent scar formation, and is capable of being widely applied to rapid hemostasis, moisture retention, emergency, and treatment of burns and prevention of scar formation.