Understanding the spatial and temporal variation characteristics of atmospheric water resources in each region of China is essential for their exploitation. In this study, we focus on the variation in atmospheric precipitable water (PW), cloud parameters, cloud water resources (CWR), and precipitation efficiency of hydrometeors (PEh) as well as their possible influencing factors in each region of China in summer using ERA5 and MODIS data. The results showed that: (1) In the past 42 years, PW increased significantly in the northwest and Tibetan Plateau regions, and both cloud cover and total column cloud water content decreased significantly in northern China, except for medium-cloud cover which significantly increased in the Tibetan Plateau. (2) In the past 20 years, annual PEh was significantly higher, with clear interdecadal variation in most regions, whereas CWR decreased in northern China, the southwest, central region, and southeast, and increased in northeast and Tibetan Plateau. (3) PEh in each region was greatly influenced by precipitation (correlation coefficient 0.55 < R < 0.82 *, * = p < 0.05), having a significant positive correlation in the northeast with cloud water path, cloud optical thickness, and aerosol optical depth (0.44 * < R < 0.54 *), and a significant negative correlation in the central region with the cloud effective radius (R = −0.54 *).