Abstract: The Yalong River Basin is one of the key regions for hydropower development in China. Exploring the temporal and spatial evolution characteristics of dry and wet condition of the basin in the context of global climate change is conducive to rational planning and full use of water resources, providing scientific guidance for agricultural production activities in the basin. Based on the monthly meteorological data of 16 meteorological stations in and around the Yalong River Basin from 1981 to 2017, the potential evapotranspiration ET0 of each station was calculated using the Penman-Monteith (PM) formula. The corrected CHIRPS satellite precipitation products with higher spatial resolution is used to calculate the standardized precipitation evapotranspiration index SPEI. The cloud model and Mann-Kendall (MK) trend test are used to analyze the spatial and temporal distribution characteristics and trends of the inter-decadal, annual and seasonal scales. The results show that: (1) The deviation correction of the CHIRPS satellite precipitation product not only improves the accuracy, but also obtains the precipitation with higher spatial resolution; (2) the spring is humidified in the basin, and the other time scales show a trend of drought. The rate of aridification is the fastest in winter. The stability of the wet and dry variation in the annual scale is the worst, and the stability in autumn is relatively best. The spatial distribution of SPEI in spring and winter is weaker than the time distribution. (3) The relative dry and wet areas of the watershed at the same time scale are approximately normal, and the spatial distribution of dry and wet changes in the basin is quite different; (4) There is no obvious regional distribution pattern in the drought and wetting high-incidence areas of all levels in the basin. The highest frequency of drought and wetting is about 20%, and the frequency change range is gradually reduced with the increase of dryness and wetness; (5) Frequency difference of wet and dry in different ages is more significant. The annual average drought frequency change shows decrease-increase-decrease trend, the wet frequency change shows increase-decrease-decrease trend, and wetting high-incidence areas transferred from downstream to upstream.