Rainfall erosivity (R) is an important index for evaluating soil detachment and transport erosion, reflecting the potential ability of rainfall to erode soil. It is important to explore the evolution of R at the centennial scale to determine regional ecological security patterns. Based on the monthly rainfall data from the CRU_TS4.01 dataset, R in southwestern China from 1901 to 2016 was calculated in this paper and we further analyzed the evolution of the spatiotemporal pattern and pixel-based trend dynamics. Major findings are as follows:1) The spatial distribution of R in the southwestern China has been consistent with the distribution of rainfall, showing a spatial pattern that gradually increased from northwest to southeast. 2) In southwestern China, 34.11% of the region has a mean annual R of 4500 to 5500 MJ mm hm^-2h^-1 a^-1. 3) R in southwestern China is highly concentrated during the year. The accumulated R in summer (June to August) and autumn (September to November) in each region accounted for 75.84% to 96.09% during the year. The seasonal maximum rainfall erosivity occurred in summer in the Nyingchi region of Tibet, with a contribution rate of 74.2%. 4) The mean value of R in southwestern China is 4098.84 MJ mm hm^-2h^-1 a^-1, the highest level (appeared in 1915) was 4667.75 MJ mm hm^-2h^-1 a^-1, and the lowest level (appeared in 1992) was only 3936.63 MJ mm hm^-2h^-1 a^-1. 5) Spatial heterogeneity in R was found in southwestern China for 47.59% of the regions presenting a decreasing pattern and 32.91% that showed an increasing dynamic. This study provides theoretical and statistical references for the prevention and control of soil erosion, as well as the formation and evolution of ecological security patterns in southwestern China.