To improve the current and output power of terahertz Traveling Wave Tube(TWT), a Fundamental Mode Multi-Beam Folded Waveguide(FMMBFW) TWT scheme is proposed. Firstly, the high frequency characteristic is gained and compared with numerical simulation result. Secondly, the transmission characteristic of 60 periods FMMBFW is analyzed. Lastly, the beam-wave interaction characteristic of 0.14 THz FMMBFW TWT is completed by numerical simulation and theoretical calculation. When the DC current is 12 mA and the voltage is 15.75 kV, the 3 dB band of 0.14 THz FMMBFW TWT is 25 GHz(128 GHz-153 GHz), the maximum gain is 33.61 dB and the maximum output power is 23 W. When the DC current is 30 mA and the voltage is 15.75 kV, the maximum gain is 38 dB and the maximum pulse output power is 63.1 W at 0.14 THz. This method can effectively increase the current of FMMBFW TWT, and the interaction gain, efficiency, 3 dB band, output power can be improved. When the gain is the same, FMMBFW TWT can be fabricated more short and compact.