In the normal gate CNT-FED, the gate electrode is used to modulate and address the electron beam. Some electrons may bombard on the gate electrode, thus the luminant efficiency of CNT-FED decreases. This paper proposes a new gate structure, which is the metal mesh with cone funnels. MgO film and MgF2 film are vaporized on the surface of the mesh and the funnels. When the primary electrons bombard on the gate electrode with initial energy, the secondary electrons and backscatters are generated. As results, more electrons can pass through the gate electrode and land on the anode. Consequently, the brightness of the novel triode structure CNT-FED can increase obviously. In the paper, we show the results of numerical simulation of the secondary electron emission process with Monte Carlo method. Some CNT-FED devices with the new type of gate structure are fabricated. The surface of the gate electrode is coated with MgO, MgF2 and SiO2 film, respectively. The results of emission experiments are also shown in this paper.