The invention relates to a catalyst used in preparation of low-carbon olefins by using synthesis gas and a preparation method and application of the catalyst. The catalyst comprises a main active ingredient and a co-active ingredient, wherein the main active ingredient is ferric oxide and zinc oxide, and the co-active ingredient is potassium hydroxide or magnesium carbonate. The method for preparing the catalyst is shown in the specification. The catalyst has the advantages that the low-carbon olefins are obtained directly by the synthesis gas without an intermediate product such as methanol, so that the low-carbon olefins are low in production cost and high in selectivity; and a separation flow is simple, the per-pass conversion rate of CO is high, the production capacity of methane and CO2 is low, and the operation energy consumption is low. The catalyst is used in synthesis of the low-carbon olefins directly by using the synthesis gas.