The intensity distribution of a yellow luminescence band was observed by cathodoluminescence (CL) on GaN epilayers with different surface morphologies grown by metallorganic vapor phase epitaxy, which showed that the hexagonal hillock surface morphology had an effect on CL image of the yellow luminescence band. The polished epilayers were further investigated by CL image, atomic number contrast, and wavelength dispersive X-ray spectrometry, and were observed that the intensity of the yellow luminescence band was relatively strong around the defects associated microscope exhibited the structures of the defects different from that of GaN matrix, misfit edge dislocations and cracks. The results suggest that the defects may result from the precipitations in the V-shape grooves of imperfect coalescence during epitaxy.