G-band Traveling Wave Tube(TWT) mainly uses the high-frequency structure to amplify and radiate the high-frequency electromagnetic wave. The output window is one of the main components in the high-frequency system of a traveling-wave tube. The quality of its design affects the normal output and radiation of high-frequency waves, particularly in terms of critical parameters such as window dimensions or waveguide length. To detect potential failure during actual operation, reliability analysis of the output window structure must be conducted to validate its robustness. This paper presents the design of an output window for a G-band hundred-watt TWT, along with its simulation and experimental S-parameter results, and those results are in agreement with each other. To verify the structural reliability of the designed output window, comprehensive thermal analysis and vibration analysis were performed. Corresponding modal and random vibration analysis results are provided, demonstrating that its Margin of Safety(MS) meets specified requirements.