The invention relates to an external use ointment used for treating dermatitis and a preparation method thereof. An effective compound of the external use ointment comprises following raw materials: caragana microphylla, sundew, alternanthera sessilis, convolvulus arvensis, excoecaria sebifera, acronychia leaf, wing nut leaf, kazinoki broussonetia, calamint, gingium verum, vitex trifolia, ferb of desertliving asparagus, chenopodium album seed, mosla scabra, fruit of siberian nitraria and lantana camara. The external use ointment has efficacies of clearing heat and removing toxicity, eliminating dampness and relieving itching, and coursing wind and nourishing blood; and has significant effects on treatment of allergic dermatitis, atopic dermatitis, neurodermatitis, seborrheic dermatitis and dermatitis medicamentosa; possesses excellent curative effects on common dermatitis diseases such as erythema, papule, rahagades, desquamation, small abscess, pruritus, tenderness and burning heat sensation; and is capable of killing bacteria on human skin surface rapidly and efficiently, removing corrupted materials, promoting optimization and growth of epidermis cells effectively, enhancing plastid of epidermis cells, and helping damaged human body to recover rapidly.