We fabricated AIN thin film by using RF magnetron sputtering and studied the structural characteristic of AIN thin film with the change of the deposition conditions such as Ar/$N_2$ flow ratio, working pressure, and the distance between substrate and target. The orientation and surface roughness of AIN thin film were studied by using XRD and AFM. We can not identify the orientation of the thin film deposited in Ar, while we obtained the (l00) orientation of the thin film with the addition of $N_2$. Especially, the thin film deposited at 18/2 (seem) of Ar/$N_2$ flow ratio exhibited to be the most (100) oriented. The (100) orientation of thin film becomes weaker as the working pressure becomes higher. The further distance between substrate and target is stronger the (100) orientation of the thin film, but the (100) orientation becomes weaker and (002) orientation started to appear as the distance is shorter. The surface roughness of the thin film deposited at 50$0^{circ}C$ in Ar only is 1.1 nm, while very smooth thin film of 0.4～0.6 nm is obtained with the addition of $N_2$.