In this work, we demonstrated the use of a promising sensor based on alumina Photonic Crystals (PC) which can be applied in the field of gas detection owing to the well structured PC with an ultra-narrow Photonic Bandgap (PBG), of which the full width at half maximum is only 30 nm. This type of PC was prepared successfully by using a compensation voltage mode method, which can effectively compensate for the chemical corrosion and the slowing down of ion exchange, resulting in a uniform diameter of the pores in the anodic alumina oxidation (AAO) from beginning to end. The as-prepared sample was applied to detect the concentration of organic vapor, such as ethanol, in this experiment. A large PBG shift is achieved when the concentration of ethanol changes, and the mechanism was also discussed theoretically. This sensor had a good repeatability due to the chemical and physical stability of the matrix material (alumina). These results indicate the potential applications of the as-prepared AAO based PC in the sensing field.