The invention relates to a medicine for treating gastric diseases and a preparation method thereof. The medicine is prepared from the following medicinal raw materials by weight: 15g of astragalus membranaceus, 15g of cassia twig, 15g of semen arecae, 15g of rhizoma cyperi, 15g of rhizoma corydalis, 15g of coix seed, 15g of radix paeoniae alba, 6 pieces of Chinese date, 50g of raw ginger, 15g of fructus amomi, 50g of honey and 15g of fingered citron. The preparation method comprises the following steps: a, grinding fructus amomi, rhizoma cyperi and radix paeoniae alba into medicinal powder; b, decocting astragalus membranaceus, cassia twig, betel nut, rhizoma corydalis, coix seed, Chinese date, raw ginger, honey and fingered citron for three times, and decocting for two hours each time, combining the three decoctions, and preparing thick paste by adopting a decompression concentration method; c, adding the medicinal powder prepared in the step a and auxiliaries into the thick paste prepared in the step b, uniformly stirring, drying, grinding into fine powder, and preparing clinically acceptable preparations according to a conventional process. The medicine is reasonable in prescription, concise in compatibility and exact in curative effect, has a good curative effect on controlling and treating gastric diseases, and does not have toxic or side effect.