The invention provides a catalyst for coproduction of mixed alcohols and alpha-olefin through a synthesis gas one-step method and a preparing method and application thereof. The catalyst is prepared from Co3O4, stable oxide of M1 and stable oxide of M2, wherein Co, M1 and M2 account for 10-60%, 0-5% and 10-60% of the total mass of the catalyst, M1 is selected from one or more of Li, Na, K, Rb and Cs, and M2 is selected from one or more of Mg, Ca, Zn, Al, Zr, Mn, La and Ce. The active component of the catalyst for coproduction of mixed alcohols and alpha-olefin through the synthesis gas one-step method is obtained for reduction activation and carbonization, and the active component is Co2C nano particles. The preparing method is simple, the obtained catalyst is high in stability, the carbon number selectivity of mixed alcohols and alpha-olefin in the synthesis gas one-step method for coproduction of mixed alcohols and alpha-olefin is high, and the methane selectivity is low.