Injector-like nanostructure samples of ZnO, which are synthesized by hydrothermal method, are experimentally investigated for the field emission (FE) properties, especially the current density varying with the intensity of the applied electric field; and the fascinating two-stage behavior of electric field enhancement factor (β) is observed. The good performance and the two-stage behavior of the β are explained based on the combination of the intensive electric field effect in semiconductor and its influence on the Fermi energy level with the effective series connection circuit of FE detection systems. Finally, the previous analysis conclusion is well experimentally demonstrated by the FE properties and PL spectra of Znic oxide nanostrucutres fabricated by electrochemically deposition and vapor phase transmitting methods, separately.