Abstract: Carbon nanotube cold cathode has excellent field emission characteristics and has potential application prospects in the electron gun of traveling-wave tubes. According to field emission theory, a sheet beam grid-controlled electron gun based on carbon nanotube cold cathode for G-band traveling-wave tubes is investigated. The electron gun is composed of a cathode, a shadow grid, a control grid, a focusing electrode and an anode. The cathode emission surface is elliptical with a semi-major axis length of 0.8 mm and a semi-minor axis length of 0.4 mm. Both grids have square mesh, while the focusing electrode has an elliptical tunnel to further compress the electron beam into a sheet beam. The electric field distribution in the electron gun and the influence of shadow grid thickness on the electron beam are analyzed. The simulation results of CST show that when the cathode voltage is -24.6 kV, the cathode emission current of the electron gun is 36.9 mA, with a range of 7.2 mm, a beam waist size of 0.52 mm × 0.15 mm, and an area compression ratio of 12.9. No current interception occurs at any electrode. This study lays a theoretical foundation for the application of carbon nanotube cold cathode to G-band traveling-wave tubes.