ZnO thin films with different thickness were prepared on glass substrates by using a sol-gel method. The effect of different sol ratio and concentration on the thermal radiation properties of the ZnO thin films was analyzed. The ZnO thin film had the best thermal radiation property and best absorption ability when its sol ratio was 1∶1 and its concentration is 0.8%. The structure and morphology of the ZnO thin film were characterized by using both X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) technologies. The results showed that the prepared ZnO thin film exhibited its hexagonal wurtzite structure with preferred orientation at (002) and had good crystallization behavior.