The invention discloses an external ointment for treating an allergy of a skin and a preparation method, and belongs to the field of traditional Chinese medicines. Effective components of the external ointment provided by the invention comprise the following raw-material ingredients in parts by weight: herba polygoni hydropiperis, folium rumex japonicus, herba Hemigraphis procumbens, folium baeckeae, herba saginae japonicae, herba arthraxon hispidus, folium prunus armeniaca, herba lemmaphyllum microphyllum, origanum vulgare, radix rumicis patientiae, herba eria pannea, herba carpesium abrotanoides, a peach leaf, salix chienii, herba cyperus rotundus and flos campsis. The external ointment provided by the invention is processed by finely selecting ingredients, which have the functions of clearing away heat, promoting diuresis, clearing away toxic materials, deswelling, dispelling wind, arresting itching, regenerating tissue, healing a wound, cooling blood, stopping bleeding, and the like, of traditional Chinese medicinal materials; all medicines are combined to directly reach a position suffered from a pathological change; the external ointment for treating allergy of the skin has advantages of being quick in effectiveness and high in cure rate, having no toxic or side effects, being safe and convenient, being lasting in curative effect, and the like, and is suitable for the popularization and the application to the clinical treatment and nursing of allergy of the skin.