The southwestern region of China, serving as an ecological barrier for the upper reaches of the two rivers and an area with continuous karst distribution, has a fragile ecological foundation. Investigating the spatiotemporal evolution and spatial spillover effects of its ecosystem service values is of significant importance for optimizing regional ecological management. This study, through ecosystem service value accounting combined with social network analysis methods, revealed the spatiotemporal evolution characteristics and spillover effects of the spatial correlation network of ecosystem services within the southwestern region. Additionally, the spatial Durbin model was employed to explore the spatial effects and driving factors of ecosystem service values between the southwestern region and adjacent areas. The results indicated that: (1) From 2000 to 2022, the overall ecosystem service value in the southwestern region showed an increasing trend, with the spatial distribution pattern of ecosystem service values in various prefectures remaining relatively stable; (2) During the study period, the mean gravitational value of ecosystem service values among prefectures increased from 0.3176 to 2.1289, and the network density increased from 0.2041 to 0.2083, indicating an enhancement in the strength of spatial correlations and the stability of the network related to ecosystem service values; (3) Block model analysis showed that the spatial correlation network of ecosystem service values could be divided into four blocks, with significant correlations and spillover effects both within and between blocks, and the level of coordinated development of ecosystem service values within each block improved; (4) The spatial spillover effects of ecosystem service values between the southwestern region and adjacent areas were significant, with Rho coefficients for the adjacency matrix and geographical distance matrix being 0.2585 and 0.5455, respectively. This suggested that for every unit increase in ecosystem service value in the southwestern region, the ecosystem service values in adjacent areas increased by 0.2585 and 0.5455 units, respectively, highlighting its ecological barrier function; (5) Precipitation, NDVI, urbanization, and industrial structure optimization promoted the ecosystem service values in the study area, while cultivated land area, population density, and per capita GDP had inhibitory effects. The findings of this study can provide a scientific basis for regional ecological restoration, ecological zoning control, and the enhancement of ecosystem service functions.