The first-principles calculations based on the density functional theory have been performed to investigate the doping behaviors of Na and F dopants in ZnO. It turns out from the calculated results of the band structure, density of states, and effective masses that in the F mono-doping case, the impurity states are localized and the formation energy is up as high as 4.59 eV. In the Na mono-doping case, the impurity states are delocalized and the formation energy decreases as low as -3.01 eV. One cannot obtain p-type ZnO in both instances On the contrary, in the Na-F codoping case, especially when the ratio of F and Na is 1:2, the Fermi-level shifts to the valence bands, the corresponding effective masses are small (0.7m0) and the formation energy is the lowest (-3.55 eV). These may indicate the formation of p-type ZnO having a good conductivity.