The invention provides a medicated bath lotion for pigs. The medicated bath lotion is prepared from, by mass, 20-30 parts of semen brassicae, 2-4 parts of pumpkin seeds, 15-20 parts of radix aucklandiae, 15-25 parts of callicarpa macrophylla Vahl, 15-18 parts of lily, 2-4 parts of ground pepper, 6-8 parts of fructus citrus sarcodactylis, 3-5 parts of crowndaisy chrysanthemum, 8-10 parts of arundina graminifolia, 4-6 parts of herba asari, 15-25 parts of cortex meliae, 12-15 parts of Chinese pulsatilla roots, 3-6 parts of peach kernels, 3-5 parts of wampee bark, 3-5 parts of rhizoma pinelliae, 4-6 parts of fructus amomi, 1-3 parts of wrinkled gianthyssop herb, 15-20 parts of fructus quisqualis, 4-6 parts of silkworm excrement, 3-5 parts of flos chrysanthemi indici and 2-6 parts of rhizoma cyperi. The invention further provides a preparation method of the medicated bath lotion. The medicated bath lotion is convenient to use; in the use process, it is only needed to add the medicated bath lotion into warm water according to the portion that 7 kg of medicated bath lotion is added into each 10 kg of water, the mixture is stirred to be uniform, and then a medicated bath can be conducted. By means of the medicated bath lotion, the body surfaces of sows can be comprehensively cleaned and deodorized, and meanwhile a good parasite expelling effect can be achieved.