Mainly works on the controlled synthesis, properties and applications of carbon nanotubes and their composites. An in situ TEM method is developed to investigate the growth mechanism of carbon nanotubes. Enriched metallic/semi-conducting carbon nanotubes are controllably prepared using combined catalyst design and in situ selective etching. High-quality carbon nanotube films, fibers, vertically aligned arrays and their hybrids are designed and prepared, which show excellent transparent conductive performance, high thermal conductivity and good thermoelectric property. Explore the application of carbon nanotubes and their composite in flexible electronics, electrochemical energy storage, optoelectric devices, etc.