The semiconducting property of carbon nanotubes have been investigated by the luminescence measurement. The morphology of carbon nanotubes has been detected by the scanning electric microscope, and the X ray diffraction determines the atomic structure of carbon nanotubes. The carbon nanotubes can be luminescence under laser irradiation. Using the photoluminescence measurement, the emitting spectrum of carbon naotubes is very spread in a near-red emission range and a main peak at 1.3 eV . The temperature dependent of photoluminescence effect indicates that the semiconducting property of carbon nanotubes is very clearly. According to the thermally photoluminescence experiment, the luminescent property of carbon nanotubes is due to the center of energy trap of defect. It is suggested that the luminescence of the semiconducting property result is dominated by the electron trap of defect in the carbon nanotubes system.