The invention belongs to the technical field of chemical catalysts and relates to a catalyst for preparing isobutene through isobutane dehydrogenation and a preparation method thereof. 0.5-10.0% by mass of silicon oxide is added into an alumina carrier, then the alumina carrier is loaded with vanadium oxide with a vanadium content of 3.0-11.0% by mass and then 0.1-5.0% by mass of an alkali metal or an alkaline earth metal as a cocatalyst is added into the alumina carrier. Silicon oxide is introduced into the alumina carrier so that an alumina carrier pore structure and surface properties are improved and vanadium oxide active site distribution is changed. Through use of an alkali metal and an alkaline earth metal, catalyst surface pH and electron properties are improved, a conversion rate and selectivity of isobutane dehydrogenation preparation of isobutene are improved and a catalyst service life is prolonged.