To achieve an optimum cold cathode emitter, well-aligned TiO2/Ti nanotube arrays (TNAs) were synthesized by anodic oxidation and doped with carbon by pyrolysis of C2H2 at 550 °C. By controlling the carbon doping content, the field emission (FE) properties of carbon-doped TiO2/Ti nanotube arrays (C-TNAs) were optimized. Compared with the high turn-on field of 19.19 V/μm from pure TNAs, the turn-on field of C-TNAs was decreased to 11.60, 6.35, 4.10, and 5.77 V/μm when the doping content of carbon was increased to 0.62, 0.82, 1.81, and 3.31 at. %, respectively. Obviously, the FE properties of TNAs were dramatically improved and optimized by adjusting the carbon doping content, which can be attributed to the typical tubular morphology, an enhanced conductivity, and a reduced work function.