This invention relates to a method of preparing a multicomponent bismuth molybdate catalyst by changing the pH of a coprecipitation solution upon coprecipitation and a method of preparing 1,3-butadiene using the catalyst. The multicomponent bismuth molybdate catalyst, coprecipitated using a solution having an adjusted pH, the preparation method thereof, and the method of preparing 1,3-butadiene through oxidative dehydrogenation using a C4 mixture including n-butene and n-butane as a reactant are provided. The C4 raffinate, containing many impurities, is directly used as a reactant without an additional process for separating n-butane or extracting n-butene, thus obtaining 1,3-butadiene at high yield. The activity of the multicomponent bismuth molybdate catalyst can be simply increased through precise pH adjustment upon coprecipitation, which is not disclosed in the conventional techniques. This method can be applied to the increase in the activity of multicomponent bismuth molybdate catalysts reported in the art.