Field emissions of wide-band-gap-material (WBGM)-coated single-walled carbon nanotubes (SWCNTs) were studied. Field emission current was gradually increased after monolayer coating (MgO-coated SWCNTs) and successive double layer coating (CsI/MgO-coated SWCNTs). The turn-on field decreased from 3.26 to 2.43 and 1.61 μA cm-2, respectively. The calculated work functions were found to be 3.34 and 3.01 eV, and the maximum secondary electron emission yields were 115 and 40 for MgO- and CsI/MgO-coated SWCNTs, respectively. These results would be due to a higher electric field generation around the SWCNT surface after double layer WBGM coating rather than single layer WBGM coating. To reveal the influence of WBGM coating on carbon nanotubes, x-ray photoelectron spectroscopy and energy dispersive analysis of x-ray spectra were analyzed.