In previous studies, the p-n junction effects on the field emission currents of the narrow- and wide-band-gap one-dimensional nanostructures grown on n-type and ptype doped silicon substrates are demonstrated experimentally and explained qualitatively by the Schottky barrier effect . But the detailed band structures near the nanostructure-substrate interface under equilibrium and strongly external biasing conditions are not clear yet. In this paper, the field emission properties of the onedimensional nanostructure grown on doped silicon substrate will be studied via computer simulation. Our simulation model is shown in figure 1. The classical transport equation is used to describe the carrier transportation in the material and is solved coupled with the Poisson's equation  . The field emission process between emitter and vacuum interface is modeled by the Fowler-Nordheim equation . For studying the space-charge screening effect, the carriers are allowed to move in the vacuum region, and the space-charge fields of the carriers are also solved selfconsistently through the Poisson's equation. After the simulation, the F-N plot, the carrier distribution and the band structures are figured out. Figure 2 shows the simulation results of the anode current as a function of the applied voltage for single SiCN grown on n- and p-type doped silicon substrates. Our simulation results exhibit that the p-type substrate will limit the emission currents of the narrow- and wideband-gap nanostructure at the high-field region. And the space-charge screening effect will further saturate the emission current.