The invention discloses a cobalt carbide based catalyst used for directly preparing olefin from synthesis gas, and a preparation method and an application thereof. The preparation method comprises the following steps: 1) mixing a cobalt source with water or a cobalt source and an electronic auxiliary with water, thereby acquiring a first solution; mixing a precipitator and water, thereby acquiring a second solution; 2) adding the first solution and the second solution into water or water and the structural auxiliary, precipitating, crystallizing, separating, drying and roasting; 3) reducing the solid acquired from the step 2) in a reducing atmosphere, and then carbonizing in a carbonizing atmosphere. The preparation method is simple, the prepared catalyst is excellent in selectivity and the conversion rate is high.