[Objective] Taking the Pearl River source region，a typical karst area，as the research object，this study aimed to construct a reasonable ecological security pattern，analyze the evolution of the ecological security pattern from 1990 to 2020，and provide scientific support for strengthening biodiversity conservation and ecological restoration in karst regions. [Methods] Based on the evaluation of ecosystem service importance and ecological sensitivity，in combination with methods such as MSPA，MCR，and the gravity model，the ecological security pattern of the Pearl River source region from 1990 to 2020 was constructed，and its spatial-temporal evolution characteristics were analyzed. [Results] 1）Ecological sources were concentrated in the southern part of Qujing City and the border with Wenshan Prefecture，while they were scattered in the western part of Yuxi City，the border of Kunming City with Qujing City and Honghe Prefecture，the southern part of Honghe Prefecture，and the northeastern part of Qujing City. From 1990 to 2020，the area of ecological sources showed a trend of increasing first and then decreasing，and reaching a maximum in 2000. 2）The comprehensive resistance surface exhibited obvious spatial heterogeneity，and the area and range of high-resistance zones had been continuously expanding from 1990 to 2020. 3）In 1990 and 2000，55 ecological corridors were identified，which decreased to 45 in 2010 and 2020. Important ecological nodes were mainly distributed in ecologically sensitive areas such as the border of Qujing City，Yuxi City，and Honghe Prefecture. 4）The overall structure of the ecological security pattern in the Pearl River source region was consistent with the direction of rivers，but due to human activities，the ecological security pattern in the Nanpan River Basin was fragile. [Conclusion] Urbanization，land use change，and increased intensity of human activities are the main factors affecting the evolution of the ecological security pattern in the Pearl River source region. In the future，focus should be placed on protecting key ecological sources， restoring and constructing ecological corridors， developing eco-friendly industries， and establishing a comprehensive ecological monitoring network to improve the stability and sustainability of the karst ecosystem.