The invention discloses a medicament for treating cattle/pig constipation, and a preparation method thereof. The medicament is prepared from rhubarb, immature bitter oranges, magnolia officinalis, fructus cannabis, bunge cherry seeds, mirabilite, figwort roots and radix rehmanniae according to a certain mixture ratio by weight. The medicament has the efficacy in clearing heat, releasing toxin, purging pathogenic fire, dispelling fire stasis in large intestines, promoting blood circulation, removing blood stasis, relieving constipation, invigorating gallbladder and eliminating abdominal distension/pain, has the advantages of short treatment course, remarkable therapeutic effects, low cost, high cure rate and no relapse, and is widely used for treating cattle/pig constipation.