In this paper, carbon nanotubes synthesized by floating catalyst method were purified by liquid-phase oxidation method and treated by hydrogen plasma with different time. The morphology and microstructure of carbon nanotubes were characterized by transmission electron microscope (TEM), high-resolution transmission electron microscope (HRTEM), selected area electron diffraction (SAED) and Raman spectroscope. The results showed that carbon nanotubes with bamboo-like structure changed solid and helical structure with the treatment of hydrogen plasma for 5 h and 10 h, and the intensity of D peak in Raman spectrum was larger and larger. The UV-vis absorption spectrum indicated that the absorption peak of treated carbon nanotubes was redshifted, stronger and narrower than that of untreated carbon nanotubes. However, the effect of hydrogen plasma treatment on the FT-IR spectrum of carbon nanotubes was slight. The results probably made carbon nanotubes have important applications in optical absorption material with controllable wavelength. (C) 2007 Elsevier B.V. All rights reserved.