The invention discloses a drug for treating diabetics and a preparation method and application thereof; the drug is prepared from, by weight, 3-7 parts of montmorillonite, 15-23 parts of Fructificatio Hexagoniae Apiariae, 11-19 parts of fruit of Cinnamomum bodinieri, and 1-5 parts of bulb of Fritillaria davidii; the preparation method comprises: grinding and crushing montmorillonite and fruit of Cinnamomum bodinieri, adding 45% ethanol, heating and stirring, ultrasonically treating, centrifuging, and drying in vacuum to obtain mixture A; crushing Fructificatio Hexagoniae Apiariae, extracting with water, and concentrating to obtain aqueous extract of Fructificatio Hexagoniae Apiariae; crushing bulb of Fritillaria davidii, adding edible vinegar, stirring to dryness to obtain bulb powder of Fritillaria davidii; mixing the above materials, microwave-treating, drying, and granulating. The drug has significant hyperglycemic effect, can improve heavy-headedness, weak, numbness and pain due to diabetics and various complications, has no toxic and side effects, can repair injured pancreas, liver, and kidney tissues, has good and quick action for treating diabetics, and is suitable for wide application.