The invention relates to an external drug for treating skin diseases, particularly an external ointment for treating skin diseases. The external ointment is prepared by the following steps: (1) taking Sophora flavescens, myrrh, Radix Angelicae dahuricae, Divaricate Saposhnikovia Root, and chrysanthemum, cleaning, carrying out water extraction through boiling water, filtering, condensing the filtrate into a concentrated solution, and making the concentrated solution into first fine powder; (2) taking borneol, musk, calculus bovis, pearl, and calcined calamine, respectively crushing into fine powder, and mixing uniformly to obtain second fine powder; and (3) taking Vaseline and lanolin, heating, filtering out impurities, cooling, adding the first fine powder, second fine powder, polyinosinic-polycytidylic acid and PEG, mixing uniformly until semi-solid to obtain a finished product. The external ointment has the characteristics of warming acrid, relieving exterior syndrome, clearing heat, expelling evil, moving qi, promoting blood circulation, removing blood stasis to produce new, healing sore, relieving pain, resisting virus, raising body immunity, improving blood circulation, promoting regeneration and restoration of tissues, and has good curative effect on herpes simplex, herpes zoster, genital herpes, and refractory sore and ulcer diseases.