The growth front evolution of GaN thin films deposited on sapphire substrate by hydride vapor phase epitaxity has been studied with atomic force microscope. The evolution of the surface morphology presents four features of stage with the growth process. In initial growth stage, the surface is granular, and the typical grain diameter is about 250nm for t =0.1min. 3D growth plays a key role before the films come up to full coalescence, which causes a rough surface. After 0.1min the growth dimension decreases with the increase of lateral over growth, the surface roughness obviously decreases. From 0.4min to 3min, the growth front roughness increases gradually, and the evolution of the surface roughness exhibits the characteristics of self-affined fractal. Beyond 3min, the root-mean-square decreases gradually, which means the deposition behavior from hyper-2D growth gradually turns into layer growth mode with the increase of growth time. The growth front the evolution of GaN thin films deposited on sapphire substrate by hydride vapor phase epitaxity has been studied with atomic force microscope. The evolution of the surface morphology presents four features of stage with the growth process. , and the typical grain diameter is about 250nm for t = 0.1min. 3D growth plays a key role before the films come up to full coalescence, which causes a rough surface. After 0.1min the growth dimension decreases with the increase From 0.4 min to 3min, the growth front roughness increases gradually, and the evolution of the surface roughness exhibits the characteristics of self-affined fractal. Beyond 3min, the root -mean-square increasingly gradually, which means the deposition behavior from hyper-2D growth gradient turns into layer growth mode with the increase of growth time.