The invention provides oral liquid for treating cancers and a preparation method thereof. The oral liquid is prepared from the raw materials in parts by weight: calcium sulfate, zinc sulfate, ammoniumphosphatide, sodium chloride, potassium sulfate, selenium yeast, lithium carbonate, manganese sulfate, cobalamin, copper sulfate, ferric sulfate, molybdenum trisulfate, magnesium sulfate heptahydrate, raw white vinegar, rock extraction original liquid, a fructus trichosanthis extract, artemisinin, cantharidin, titanium dioxide, a herba lobeliae chinensis extract, a herba taraxaci extract, a rhizoma pleionis extract, a rhizoma smilacis glabrae extract and the like. The oral liquid is mainly applied to the treatment of common tumors and cancers of digestive systems, respiratory systems, urogenital systems and the like, which have the highest pathogenesis rate, of human bodies.