The invention discloses an application of mannitol in preparation of an anti-stomach cancer drug, and in particular relates to a use of a mannitol injection with a specific concentration of 10%-19% for treating stomach cancer. Traditionally, mannitol is only used as a diuretic, a high-permeability hypotensor and the like, while the inventor discovers through scientific experiments that mannitol has anti-tumor activity, and through several cell apoptosis detection technologies and by detecting apoptosis-related genes bcl-2, and bax, proves that the specific-concentration mannitol can induce various human cancer cell strains to generate obvious cancer cell apoptosis, grasps the effect relation with concentration and time, and first illustrates the possible mechanism; furthermore, the inventor has used the research result for tumor patient treatment and has achieved obvious curative effect, which provides theoretical basis and practical cases for the application of mannitol in the preparation of the anti-tumor drug and the clinical generalization thereof.