The invention provides an oral medicament for treating acute lumbar sprain and a preparation method thereof. The medicament is prepared from the following components in parts by mass: respectively 1-3 parts of corydalis tuber, safflower, peach kernel, ceylon cynoglossum, sharpleaf gambirplant root, notopterygium root, sargentgloryvine stem, radix angelicae sinensis, radix paeoniae rubra, epimedium, radix salviae miltiorrhizae, eucommia ulmoides, ligusticum wallichii, radix paeoniae alba, frankincense, lycopodium clavatum, fennel and pawpaw in mass ratio. The preparation method of the oral medicament comprises the following steps: A. selecting high-quality corydalis tuber, safflower, peach kernel, ceylon cynoglossum, sharpleaf gambirplant root, notopterygium root, sargentgloryvine stem, radix angelicae sinensis, radix paeoniae rubra, epimedium, radix salviae miltiorrhizae, eucommia ulmoides, ligusticum wallichii, radix paeoniae alba, frankincense, lycopodium clavatum, fennel and pawpaw in mass ratio and then crushing into granules for laser use; and B. putting the granular medicinal materials into a cloth bag, binding the opening, putting the cloth bag filled with the medicinal materials in clean water, soaking for half an hour, putting into a drug decocting machine, injecting a proper amount of cold boiled water, decocting for 50 minutes with strong and slow fires, decocting twice, and combining to obtain 550ml of the decoction.