In this project, the design and theoretical analysis of an ultra-high sensitive breath acetone sensor based on carbon nanotube (CNT) structure is proposed. In this device, a carbon nanotube is anchored to a substrate in one end, and the other end is coated by -WO3. As a ferroelectric material, -WO3 has high selectivity in acetone absorption. The end tip of carbon nanotube is coated with -WO3 material to absorb minute acetone molecules in breath sample. Piezoelectric activation is used to activate the vibration of carbon nanotube cantilever structure. When acetone molecules are absorbed by the coated -WO3, the resonant frequency of the cantilever will be changed for a certain amount. By sensing this certain resonant frequency change, the existence of a single acetone molecule can be detected. A theoretical model is developed to describe the vibration of the carbon nanotube cantilever structure. The resonant frequency change of the cantilever due to attached mass is analyzed. The proposed breath acetone sensor can achieve extremely high sensitivity in molecular level. It can be potentially used for non-invasive diabetic's diagnosis, which leads to a quick, convenient, accurate and painless breath diagnosis of diabetics.