The invention relates to catalyst for preparing crotyl alcohol from gas-phase crotonaldehyde through selective hydrogenation and a preparation method thereof, wherein the carrier of the catalyst is one of TiO2, ZrO2 and ZnO; the active ingredient of the catalyst is a Ir-Ir3+ mixture and the mass percentage content thereof in terms of Ir is 0.5-5%; the Ir-Ir3+ mixture is loaded on the carrier and coexists as metal Ir and IrC13; and the atomic ratio of the Ir element to the Cl element in the catalyst is 1.0-1.5. The preparation method of the catalyst comprises the following steps of: firstly drying the carrier TiO2, ZrO2 or ZnO in vacuum at first, and then adding the carrier to H2IrC16 solution for soaking at the room temperature; next, evaporating the liquid to dryness in a water bath, thereby obtaining powder after drying, and then reducing the obtained powder through reduction using hydrogen, thereby obtaining the catalyst. The catalyst is high in catalytic efficiency, and good in reaction selectivity and reaction stability.