The effects of gas atmosphere and in-situ thermal annealing in buffet layers on the characteristic of the ZnO grown by RF magnetron sputtering have been investigated. It was shown that the introduction of buffer layers grown at the gas atmospheres of the mixed $Ar/O_2$ and the in-situ thermal treatment of the ZnO buffer layer improved the structural and optical properties. In addition, the ZnO films on the buffer layer thermal-annealed at $N_2$ gas ambience showed the strong emission of the near band gap exciton with narrow linewidth by combining the high-temperature growth of the ZnO film.