The invention provides a pharmaceutical composition capable of preventing the respiratory disease and diarrhoea of a pig. In the prescription of the pharmaceutical composition, sulphamethazine and plant extract of eggplant pedicles, pumpkin flowers, towel gourd roots, tobacco leaves and the like exert synergistic effect, so sulphamethazine has improved prevention effect on the respiratory disease and can prevent diarrhoea of the pig, and usage of antibiotics is reduced. Plants like the tobacco leaves, coriander, cocklebur flowers and the towel gourd root in the prescription has special smell, and addition of the plants poses influence to feed intake of the pig; however, with a production process provided by the invention, the smell of the plants is prevented from influencing the feed intake of the pig, the palatability of the pharmaceutical composition is improved, and prevention effect of the pharmaceutical composition on the respiratory disease and diarrhoea of the pig is enhanced. The pharmaceutical composition provided by the invention can effectively prevent the respiratory disease and diarrhoea of the pig without any influence on the feed intake of the live pig; and since the main components of the pharmaceutical composition are plant extract, the pharmaceutical composition has high security and can be used for a long time.