In this article, we report the study of defects between single and bulk GaN nanorods in temperature dependence. High quality of GaN nanorods have been investigated by £g-photoluminescence. Optical properties and surface morphology have been analyzed by a series of measurements, including field-emission electron microscopy (FESEM), and cathodoluminescence (CL). CL data reveal that the intensity of surface state emission is larger than near-band-edge emission at 20K . The 3.21eV peak reveals the structural defect at GaN/Si interface. The surface state emission from bottom is larger than top.