From the perspective of optical engineering application, the national cloud cover characteristics are studied, and the historical data of cloud cover in the main land areas of China in three aspects, namely, the overall average situation, the half-year change of warm and cold, and the diurnal variation, are analyzed in detail. The results show that the distribution of total cloud cover and low cloud cover in major land areas of China is basically less in the north and more in the south, and there are obvious differences in the distribution of cloud cover between the cold and warm half year, the site area where the cloud covers in the warm half year is higher than that in the cold half year is larger, and the cloud distribution difference between day and night is mainly reflected in the existence of a certaion amount of medium and high clouds in the low-value areas of low clouds during the daytime in western China.Then based on the analysis of the overall average, semi-annual and day-night variation of cloud cover, the classification of cloud cover regions in China is discussed, and it is shown that the 1 level areas suitable for optical engineering application are mainly in the north. This work is helpful to fully understand the suitable regions for optical engineering applications in whole country, and can provide support for further research on the quantitative impacts of cloud cover on optical engineering applications.