The uniform, large-scale, and bilayered ZnO nanorod array on silicon substrate has been synthesized by a catalyst and template-free chemical reaction in a dilute solution. The effect of different precursor ZnO films on the morphology and size of the ZnO nanorod array has been investigated. Moreover, the morphology evolution of the ZnO nanorod array with the increase of reaction time indicates that the second growth is the reason for the decrease of the ZnO nanorod diameter and the formation of the bilayered ZnO nanorod array. Finally, the field emission from the ZnO nanorod array with different diameters is presented.