GaN microcrystalline grains were grown by hot-wall chemical vapor deposition on Si (111)substrate. These grains with diameters of 2- 4 μm were detected by scanning electron microscopy. X- ray diffraction,Fourier transformation infrared transmission spectroscopy and photoluminescence were used to analyze the structure, composition and the optical properties of the samples. The results show that the microcrystalline grains are hexagonal wurtzite GaN,and the property of the grains was greatly affected by the growth time.