Provided is a catalyst system for oxidative dehydrogenation, a reactor for preparing butadiene including the catalyst system, and a method of preparing 1,3-butadiene. In the catalyst system for oxidative dehydrogenation, a coating catalyst is diluted with a specific dilution filler and a reactor is filled with the diluted catalyst, or a reactor is filled with a catalyst for oxidative dehydrogenation so that the concentration of an active ingredient included in the catalyst gradually increases in the direction from reactants inlet in which reactants are fed into the reactor to products outlet. The catalyst system for oxidative dehydrogenation can efficiently control heat generated inside a reactor, thereby improving conversion rate, selectivity, yield, and long-term stability of a catalyst.