The invention discloses an oral 
drug for treating hydrarthrosis and a preparation method thereof. The oral 
drug comprises, by 
mass, 1-3 parts of whole Chinese angelica, 1-3 parts of 
ligusticum wallichii, 1-3 parts of 
cyathula root, 1-3 parts of pubescent 
angelica root, 1-3 parts of poria cocos, 1-3 parts of rhizoma alismatis, 1-3 parts of root of three-nerved spicebush, 1-3 parts of safflower, 1-3 parts of 
pangolin, 1-3 parts of dried orange peel, 1-3 parts of bitter orange and 1-3 parts of licorice root. The preparation method comprises selecting high-quality and clean first order whole Chinese angelica, 
ligusticum wallichii, 
cyathula root, pubescent 
angelica root, poria cocos, rhizoma alismatis, root of three-nerved spicebush, safflower, 
pangolin, dried orange peel, bitter orange and licorice root according to the above 
mass part ratio, respectively removing impurities and dust, putting the materials into a cloth bag, tying the opening of the cloth bag, immersing the bag with the drugs in cold boiled water for about 30min until the water permeates the 
drug tissue, putting the immersed drugs and the 
clear liquid obtained by drug immersion into a decoction 
machine together, pouring cold boiled water into the decoction 
machine until the 
water level is 35mm higher than the drug level, carrying out primary decoction for 40min, carrying out 
filtration, collecting the filtrate, pouring tepor boiled water into the drugs until the 
water level is 30mm higher than the drug level, carrying out secondary decoction for 35min, mixing the decoctions obtained by the two decoction processes, and carrying out concentration to obtain 1620ml of 
traditional Chinese medicine soup with a concentration of 50%.