The invention relates to an oral medicine for treating asthma, and a preparation method thereof, and aims to solve problems that traditional Chinese medicine takes effect slowly while the curative effect of western medicine can not meet patients' satisfaction. The oral medicine is prepared by raw drug materials according to the following weight ratio: 150-300 of pheretima, 2.5-5 of promethazine hydrochloride, 20-50 of radix asteris, 50-100 of white ammonium chloride, 20-50 of radix stemonae, 56-112 of extractum glycyrrhizae, 1-2 of camphor and 1-2 of star anise oil. The preparation method comprises the following steps of (1) smashing a specified amount of pheretima, promethazine hydrochloride, radix asteris, white ammonium chloride, radix stemonae, and camphor into fine powder respectively; and (2) mixing the smashed raw drug materials with a specified amount of extractum glycyrrhizae and star anise oil thoroughly, and making into tablets, pulvis and capsules or other oral preparations. The oral medicine has the functions of relieving asthma, tranquilization, moistening lung to relive cough and resisting allergy, can be used for treating bronchitis, emphysema and asthma, takes effect quickly, and has high cure rate.