A method of preparing butadiene, comprising: a step of obtaining oxidative dehydrogenation reaction products containing butadiene, which are generated when reaction raw materials containing butene, oxygen (O 2), steam, and a diluent gas are passed through an oxidative dehydrogenation reaction part; a step of separating water from the oxidative dehydrogenation reaction products containing butadiene by passing the oxidative dehydrogenation reaction products through a cooling separation part; a step of condensing hydrocarbons by passing the oxidative dehydrogenation reaction products, from which water is separated, through a condensation separation part; a step of separating COx, O 2, and a noncombustible diluent gas by passing oxidative dehydrogenation reaction products containing hydrocarbons not condensed in the condensation separation part through an absorption separation part under conditions that a noncombustible diluent gas is fed; and a step, in which crude hydrocarbons comprising n-butane, butene, and butadiene, which are condensed in the condensation separation part, are passed through a purification part to separate butadiene, or the crude hydrocarbons are passed through a degasification part to additionally separate COx and O 2, and then the crude hydrocarbons are passed through the purification part to separate butadiene, wherein a gas containing n-butane remaining after butadiene is separated in the purification part is fed again into the oxidative dehydrogenation reaction part; a discharge stream containing butene remaining after butadiene is separated in the purification part is mixed with butene supplied as a raw material and fed into the oxidative dehydrogenation reaction part; and the diluent gas is butane. a step of obtaining oxidative dehydrogenation reaction products containing butadiene, which are generated when reaction raw materials containing butene, oxygen (O 2), steam, and a diluent gas are passed through an oxidative dehydrogenation reaction part; a step of separating water from the oxidative dehydrogenation reaction products containing butadiene by passing the oxidative dehydrogenation reaction products through a cooling separation part; a step of condensing hydrocarbons by passing the oxidative dehydrogenation reaction products, from which water is separated, through a condensation separation part; a step of separating COx, O 2, and a noncombustible diluent gas by passing oxidative dehydrogenation reaction products containing hydrocarbons not condensed in the condensation separation part through an absorption separation part under conditions that a noncombustible diluent gas is fed; and a step, in which crude hydrocarbons comprising n-butane, butene, and butadiene, which are condensed in the condensation separation part, are passed through a purification part to separate butadiene, or the crude hydrocarbons are passed through a degasification part to additionally separate COx and O 2, and then the crude hydrocarbons are passed through the purification part to separate butadiene, wherein a gas containing n-butane remaining after butadiene is separated in the purification part is fed again into the oxidative dehydrogenation reaction part; a discharge stream containing butene remaining after butadiene is separated in the purification part is mixed with butene supplied as a raw material and fed into the oxidative dehydrogenation reaction part; and the diluent gas is butane.