This paper studies power dependent photoluminescence spectra, the stimulated emission occurring at ultraviolet (UV) band instead of the green emission band of ZnO nanowires, which are prepared with a chemical reduction method.The dynamics of the UV emission and green emission is given to demonstrate the reason of stimulated emission occurring at UV band but not the green emission band under high excitation, which indicates that the slow decay rate of trap state makes it easy to be fully filled and saturated, while the fast decay rate of near-band-edge exciton state makes the UV emission dominate the radiative recombination under high excitation. The UV emission, as well as the corresponding stimulated emission, occurs in competition with the green deep-trap emission. In addition, when pump fluence further increases, the multiple lasing modes appear. The dependence of these lasing modes on the pump fluence is first discussed.This diagram should be helpful to understand and design the optical nanodevices of ZnO nanowires.