Screening effect and reliability are two of the most important issues in carbon nanotube-based field-emission devices. A thin Ti capping layer has been deposited on the hydrogen-pretreated catalytic iron nanoparticles to control the density of subsequently grown carbon nanotubes. In this way, the screening effect can be remarkably reduced due to the density of carbon nanotubes down to 107 from 109 cm-2 as compared to the control specimens. Thus, the turn-on field can be improved to be 2.1 from 3.8 Vμm at the emission current density of 10 μA cm2. Furthermore, the electrical breakdown field can be increased to more than 7 Vμm and the lifetime of carbon nanotubes at high electric field (10 Vμm) can be greatly prolonged from a few seconds to more than 1 h. This can be attributed to better adhesion and lower contact resistance between the carbon nanotubes and the substrate.