This paper designed an edge-aligned staggered double-vane traveling-wave tube (EASDV-TWT) at G-band. By analyzing the coupling impedance of the single period structure, the fact that the EASDV-TWT mentioned in this paper can truly strengthen the beam-wave interaction has been proved. Then, by optimizing the size of the structure and using the efficiency improving methods, a high-power EASDV-TWT has been designed. In the range of 220–240 GHz, output power is over 70 W and the gain can exceed 31 dB. In addition, the pencil-beam electron-optical system (EOS) matched to the designed EASDV-TWT has also been given in this paper to illustrate that the designed scheme is correct and achievable. This paper demonstrates the potential and feasibility of the EASDV-TWT in high-power terahertz source.