Abstract: Based on the measured monthly precipitations of 38 meteorological stations in Xizang from 1981 to 2020, the spatial and temporal characteristics of flood season precipitation(P₅₉) in recent 40 years were analyzed by using the linear trend estimation, correlation coefficients, dominance analysis, and five mutation tests such as Mann-Kendall and Cramer. The results show that: (1) The average P₅₉ of each station in Xizang showed a decreasing distribution from east to west. Compared with those in the period of 1981—2020, the average values of 84.2% stations were more in the period of 1991—2020, especially in Gêrzê. (2) The P₅₉ of 78.9% stations increased with a rate of 1.2~31.9 mm·10a⁻¹ over Xizang in the past 40 years, while the P₅₉ of 55.3% stations decreased at a rate of 0.6~42.2 mm·10a⁻¹ in the past 30 years (1991—2020). The altitude was the dominant factor of the change trend of P₅₉, the P₅₉ decreased in area below 3640 m, and increased in area above 4000 m. (3) In recent 40 years, the average P₅₉ of 38 stations increased by a rate of 10.2 mm·10a⁻¹ in Xizang, mainly in May and July. The P₅₉ showed decadal variation with a significant decrease in the 1980s, a significant increase in the 1990s, a slight decrease in the 2000s, and a normal in the 2010s. The P₅₉ showed a sudden climatic change from more to less around 2005. There was a significant period of about 3 a in flood season and monthly precipitation.