A method of producing 1,3-butadiene by the oxidative dehydrogenation of n-butene using a continuous-flow dual-bed reactor designed such that two kinds of catalysts charged in a fixed-bed reactor are not physically mixed. More particularly, a method of producing 1,3-butadiene by the oxidative dehydrogenation of n-butene using a C4 mixture including n-butene and n-butane as reactants and using a continuous-flow dual-bed reactor in which a multi-component bismuth molybdate catalyst and a zinc ferrite catalyst having different reaction activity in the oxidative dehydrogenation reaction of n-butene isomers (1-butene, trans-2-butene, cis-2-butene).