The invention discloses a drug for treating thrombophlebitis and a preparation method thereof. The drug comprises the following raw materials: coix seed, sargentodoxa cuneata, red sage root, rhizoma sparganii, red yeast rice, smilax perfoliata, salted phellodendron, earthworm, Chinese violet, evodia lepta, sansevieria, euphorbia humifusa, Indian rorippa herb, rhaphidophora decursiva, buck grass, madder, caesalpinia sappan, smilax glabra, sticktight, anemarrhena, large-leaved gentian, stephania tetrandra, floating pondweed, juncus effuses, ipomoea aquatic, phlomis umbrosa, glechoma longituba, fructus malvae vertillatae, fiveleaf akebia fruit, fried atractylodes, radix aristolochiae, katsumade galangal seed, ground beetle, and talcum. The drug is prepared by scientifically compounding traditional Chinese herbals with different pharmaceutical properties, has the functions of clearing heat, removing dampness, freeing collaterals, diffusing impediment, purging fire, removing toxicity, relieving pains, activating functional activities of qi, regulating qi, and harmonizing stomach, treats both the root and the symptoms, can safely and effectively treat the thrombophlebitis in a short time, moreover, the manufacturing technology is simple and convenient, the cost is low, and the relapse is difficult after healing.