Abstract: The temporal and spatial variation characteristics of the boundary layer height (BLH) and climate dryness and wetness factor (Aridity Index, AI) and their relationship in extremely arid areas are analyzed based on the ERA5 (the fifth generation reanalysis product of European Centre for Medium-Range Weather Forecasts) reanalysis data from 1950 to 2019. Results show that the BLH exhibits an average value of 695 m. The distribution characteristics of BLH are high in the east and low in the west. In addition, the BLH rises in the east and decreases in the west. The AI has an average value of 0.03. AI values increase in all directions, with the Tarim Basin and Central Gobi as the center of the low values. Meanwhile, the AI decreases in the east and increases in the west. In terms of temporal changes, the BLH fluctuates lower, and the AI increases from 1950 to 1964, 1965 to 1993, and 2010 to 2019; whereas, the BLH rises and the AI decreases from 1993 to 2009. The BLH and AI have opposite trends at different times in different substrata, with 80% of the years showing inverse phase changes. These two values are basically negatively correlated, with the strongest correlation in the western oasis subsurface, where the correlation coefficient reaches −0.79. With the rise of the BLH in the east and its decrease in the west, the AI shows that the scope of extreme arid areas has been moving eastward in the recent 70 years.