The invention relates to a catalyst for preparation of a low-carbon olefin from synthetic gas and a preparation method thereof. The catalyst mainly solves the problem that because of the Fischer-Tropsch synthesis reaction as a strong exothermic reaction, when using a fixed bed, heat removal in a reactor is difficult and temperature runaway is easily caused so that the catalyst easily loses activity and low-carbon olefin weight selectivity is low. The catalyst comprises, by weight, a) 10 to 70 parts of at least one carrier selected from Si and Ti oxides, b) 30 to 90 parts of an active ingredient containing a composition having the chemical formula of Fe100AaBbCcOx in an atomic ratio, wherein A represents one of Cu and Zn, B represents at least one of alkaline earth metals and C represents at least one of Rh and Ir. The catalyst well solves the above problem and is used for industrial production of a low-carbon olefin through a synthetic gas one-step method.