The invention relates to the technical field of chemistry and chemical engineering, which specifically relates to a novel method for preparing isobutene by iso-butane dehydrogenation; the novel method concretely comprises the following steps: making inert gas as emptying gas; making iso-butane as raw material; using V/CNTs as catalyst; processing catalytic dehydrogenation reaction at 480-620 degrees centigrade under 0.05-1.0MPa, wherein vanadium (atoms) loading mass of the V/CNTs catalyst is equal to 3-11wt%; and the gas hourly space velocity of the iso-butane is 10-1000h<-1>. According to the invention, catalyst used in a preparation method is characterized by friendly environment and relatively coat; in addition, the result of iso-butane conversion ratio and isobutene selectivity is close to a result when industrial chrome-aluminum catalyst is used.