Highly C-axis oriented nano-ZnO thin film was manufactured by RF-magnetron sputtering technique on a normal glass base. The influence of the heat treatment temperature on the ZnO thin film's morphology, microstructure and the residual stress is studied by the Scanning Electron Microscope and X-ray diffraction apparatuses. During the sputtering process, due to various factors, there may be residual stresses in thin films, which are usually to be reduced by heat treatment. It is shown that the films' quality can be significantly improved by post-deposition heat treatment. With the heat treatment, the crystal grains become larger, more compact and better-proportioned. Therefore, the surface of the thin film becomes smoother as well as with distinctly fewer holes. The spacing of crystal plane(002) and the residual stress of all the samples are clearly reduced, as compared with those ZnO samples not heat treated. Firstly, the spacings of crystal plane(002) and residual stresses are reduced when the heat treatment temperature is raised and before it reaches the minimum at 450℃. Then, some of the crystal grains grow excessively and the smoothness and the compact level are reduced and the spacings of crystal plane(002) and the residual stress are increased when the annealing temperature rises higher than 450℃. It is concluded that ZnO thin film's surface morphology microstructure and residual stresses are significantly improved at the annealing temperature of 450℃, which is very effective in the removal of the residual stress in thin films. Therefore in the process of preparing ZnO thin films by magnetron sputtering technique, oxygen could be introduced into the film by post-deposition heat treatment in the ambient atmosphere.