Terahertz waves (0.1THz~10THz) are electromagnetic waves which is between millimeter waves and infrared light. Terahertz waves due to their excellent performance, are widely applied in the fields of detection, communication, and material testing. Obtaining high-power, wide-bandwidth, high-quality terahertz sources is the basis and prerequisite for system applications. Among various types of terahertz sources, the traveling wave tube (TWT) has a significant advantage in terms of power bandwidth product and power-to-mass ratio compared to another device. This report will present the research work of terahertz traveling wave tubes carried out by National Key Laboratory of Science and Technology on Vacuum Electronics. During the development of the THz TWTs, the key laboratory has made breakthroughs in a series of key technologies. Novel slow-wave structures have been designed to enhance the interaction efficiency between electrons and electromagnetic waves. Concurrently, by employing PCM-focused sheet electron beams, the output power has been increased by more than double. Several TWTs at G-band and 340GHz have been simulated, fabricated and tested, which achieved pulsed output power of 100 W and continuous wave output power of 30 W at 220GHz, and continuous wave output power over 6 W at 340 GHz. The development of 1THz TWT is also underway.