In recent years, with the rapid development of high integration and high power electronic devices, the demand for high thermal conductivity materials for electronic devices is more urgent. Carbon nanotubes (CNTs), due to their unique one-dimensional nanostructures and excellent thermal, electrical and mechanical properties, have attracted much attention. In this paper, the status of research in preparation methods of CNTs, including graphite arc method, chemical vapor deposition method, laser evaporation method are reviewed. The thermal-conductive mechanism and heat-conductivity performance of CNTs and their composites are reported. At last, based on the existing development of carbon nanotubes, the future for thermal-conductive of CNTs composites is looked forward.