Carbon nanotube (CNT) has been found to be one of the promising semi-conducting materials for nanoelectronic devices and sensors due to its unique electrical properties. Our group has developed a spectrum sensor using a single CNT and demonstrated its performance. In this paper, a steady and high-yield CNT bandgap engineering will be discussed and it has been used to manufacture an appropriate CNT for spectrum infrared detection. The fabrication and experimental result of the CNT based spectrum sensor will be presented. The results indicated the CNT based spectrum sensors are capable to sense near-infrared (IR) signal and middle-wave IR signal in room temperature environment.