Carbon nanotubes (CNTs) are mono-dimensional carbon nanomaterials with remarkable properties. Since their discovery by Iijima, they have been found to exhibit remarkable properties in mechanical, physical, and chemical fields. However, due to their harsh synthesis conditions and limited inherent properties, the large-scale application of CNTs is challenging. With the aim of providing a reference for further research and development of carbon nanotubes, this review summarizes the currently reported methods for synthesizing carbon nanotubes, focusing on the cost-effective arc-discharge method and chemical vapor deposition (CVD) which produce high-quality carbon nanotubes with stable performance. In addition, two different directions of CNT modifications are presented, namely, CNT filling technology and CNT solubility modification. Among them, the CNT filling technology can use CNTs as templates for nanodevice fabrication and test tubes for microscopic reactions. Meanwhile, solubility modification of CNTs is the key strategy to overcome its inherent limitations and expand their application fields.