A D band Continuous-Wave(CW) Folded Waveguide Traveling Wave Tube(FWTWT) is introduced. The high compress ratio Pierce electronic gun, Folded Waveguide Slow Wave Structure(FWSWS), sapphire transmission energy window, Periods Permanent Magnetic(PPM) focus system, concentrated attenuator, single-stage depressed collector are adopted in the FWTWT. After the processes of the assemblage, welding, exhaust and magnet installation, a D band CW FWTWT is obtained. In the experiment of electron transmission ratio and signal amplification, under the electron voltage of 15.4 kV and electron transmission ration of 97%, the maximum saturated CW output power, the output central frequency, the maximum gain and 3 dB bandwidth are 7.3 W, 140.2 GHz, 24.6 dB and 3 GHz, respectively. The tube works stably and satisfies the engineering requirement in D band.