The Qinghai-Tibet Plateau is rich in hydropower resources for China, and the development of these has an important impact on the sustainable development of the plateau. However, the research on the pattern and processes of hydropower development on the plateau is still lacking. Using both field investigation and collected data, we evaluated the density and intensity of hydropower development on the Tibetan Plateau over the past 40 years. The spatial and temporal patterns of hydropower development were analyzed by applying exploratory spatial data analysis methods to study the spatial aggregation of hydropower development on the Qinghai-Tibet Plateau since 1980. The results show that: (1) Hydropower development on the Qinghai-Tibet Plateau can be divided into four stages-(i) pre-1980, at the beginning of development, with a small number of power stations and a small installed capacity; (ii) the period from 1980 to 2005, which was dominated by small hydropower developments, and the number of hydropower stations increased seven-fold; (iii) the 2005-2014 period, which saw large-scale cascade development; and (iv) post-2014, when hydropower development mode changed from quantity-led to scale-led. (2) Significant differences in hydropower development areas on the Qinghai-Tibet Plateau regarding the density and intensity of development from east to west are constantly decreasing. (3) The increase in hydropower development density in the past 40 years is mainly due to the increasing aggregation effect of hydropower development absorption in the eastern region (the aggregation effect of western counties has not been shown). (4) While low hydropower development intensity is found in most areas of the Qinghai-Tibet Plateau, attention must be given to river protection problems in the eastern high-intensity areas; failure to do so will increase the aggregation effect of hydropower development aggregation and, ultimately, affect the sustainable development of the regional development of the Qinghai-Tibet Plateau.