The field emission properties of hydrogen-adsorbed carbon nanotubes (CNTs) are studied using first-principles density functional theory. Open-ended (5,5) single-walled carbon nanotubes models with different numbers of hydrogen molecules adsorbed are built, and the adsorption energy, highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) band gap, the induced dipole moment of the model with and without applied electric field are calculated and analyzed. The calculation results reveal that the structure of carbon nanotubes with hydrogen molecules is stable under field-emission conditions, HOMO-LUMO band gap becomes narrower, the local density of states at the Fermi level increases with the adsorption of hydrogen molecules, and electrons emit more easily.