Carbon nanotubes (CNTs) are promising electron sources for field emission displays (FEDs) due to their excellent characteristics . But inherently spreading of the emitting electrons, inhibiting of emission current from focusing electrode design and the difficulty of self-aligned process hinder the CNT-FEDs from being a mature product. However, the dynode , usually used for electron multiplication from the secondary electron emission, provides an alternative way to enhance the current and to focus the electron beams, and potentially solve the above problems in CNT-FEDs. In this paper, the dynode amplified CNTs field emission device proposed by MRL/ITRI is investigated via computer simulation. The particle-in-cell finite-difference time-domain (PIC-FDTD) method  is used to study the effects of dynode on electrons' emission, amplification and movement. Our geometry model is shown in figure 1. We will compare the simulation results of the emission current, the anode current, and the current density distribution of the CNT-FEDs with and without the dynode structure. Figure 2 shows the yield of the secondary electron emitted from dynode as a function of energy of the incident primary electron for different incident angles used in the simulation . For the normal incident primary electron, the maximum yield is 5 when the energy of the primary incident electron is 300 eV. Figure 3 show the energy distribution of the secondary electron modeled in the simulation. Table 1 gives the simulation results of the emission and phosphor currents for the CNT-FEDs with and without dynode structure. Figure 4 shows the simulation results of the current density distributions. The simulation results exhibit that the dynode will reduce the emission current for screening of the anode voltage. But the secondary emission from dynode will magnify the emission current. At the same time, the electric field in dynode's cavity will confine and guide the electron beams to arrive at the phosphor on the anode plate. Therefore, the dynode amplified CNTs field emission device will improve the FEDs in brightness and resolution.