The samples of zinc oxide nano-wires and hexagonal micro-rods are fabricated by using vapor phase transport method under the almost same conditions. Their morphology and the same crystal structures are examined and characterized by scanning electron microscopy and X-ray diffraction. The photoluminescence (PL) spectra of hexagonal samples, excited by 355 nm laser pulse with excitation power density (260 W/cm2), is measured and compared with those from nano-wires with the same exciting condition at room temperature. There are a more intensive broaden violet emission peaking at 393 nm, frequency spectrum broatening, the red shift of center wavelength and an almost disappearing green band emission in the PL of hexagonal rods while an emission peaking at 382 nm, flat green emission for wires samples. The difference of PL spectra between the two kinds of samples may be attributed to the enhancement of spontaneous emission in whispering gallery modes resonators (WGMRs) by theoretical analysis based on the theory of energy bands for semiconductors, emission from excitons, and Fermi golden rules. PL spectrum measuring experiments with higher excitation power density for the same samples are arranged to verify the theoretical analysis results, which fit with experimental results well.