The invention discloses an alkane dehydrogenation catalyst containing a mixed Pt crystal. The catalyst is formed by three parts: an active component, accessory ingredients and a carrier, wherein the active component is Pt; the accessory ingredients are alkali metal and IVB group metal; a Pt-IVB complex crystal is concentrated in the carrier; a Pt-alkali metal octahedron crystal is concentrated on the surface of the carrier. The invention also discloses a preparation method of the catalyst. The method comprises the steps of firstly preparing Pt-IVB metal impregnation liquid with the acid concentration ranging from 1 to 3M, equivalent-volume impregnating onto the carrier, and standing, drying and roasting at room temperature to prepare a carrier containing a Pt-Sn crystal; then equivalent-volume impregnating Pt-alkali metal impregnation liquid with the acid concentration ranging from 0.2 to 0.8M onto the carrier containing the Pt-Sn, and standing, drying and roasting at room temperature to prepare the alkane dehydrogenation catalyst containing the mixed Pt crystal. Compared with a catalyst only containing a single crystal, the catalyst containing the mixed Pt crystal has better dehydrogenation activity, slower inactivation, and longer life.