Abstract: Controlled synthesis of carbon nanotubes (CNTs) and assembling them into macroscopic structures are of great importance to the applications of carbon nanotubes, and a deep understanding of the growth mechanism of carbon nanotubes would be an indispensable prerequisite for well\|defined synthesis in a controllable way. Here we show some of our recent progress in carbon nanotube's growth mechanism, controlled synthesis, and applications. By introducing a 13C labeling method, we revealed that the growth mechanism of the carbon nanotubes made by chemical vapor deposition (CVD) is the “extrusion model”. Serials of labels can be embedded into CNTs by tuning the composition and the flow rate of the reactive gases during the growth process, and the growth rate of CNT arrays can be calculated thereby. The fabrication of super\|aligned CNT arrays was expanded to 4\|inch wafer scale. A novel method was invented to process the raw yarn by passing through volatile organic solvents. As a result, both the strength and manipulability were improved substantially. The processed yarn can be applied as thermal electron sources, large current density field emitters and in fluorescent tubes etc. Thermal interface materials (TIMs) has significant importance in IT industry, we prepared CNT array\|polymer matrix which has very high thermal conductivity and extremely low thermal resistance. Techniques like chemical modification, tip etching and surface metal layer were explored to enhance the thermal conductivity of the CNT thermal interface materials.