Karst region is characterized by its ecological significance and vulnerability. Exploring its spatial and temporal evolution of landscape ecological security pattern will shed light on local land use management and ecological restoration. Here, we examined in depth the features of spatial and temporal evolution of land use change, landscape pattern, and landscape ecological security pattern in Karst Fault Basin at junction of Yunnan, Sichuan, and Guizhou provinces, based on five phases of land use data in 2000, 2005, 2010, 2015, and 2020 and used methods of land use transition matrix analysis, landscape pattern index, and landscape ecological security index calculation. The results were as follows. (1) In terms of land use change, forest, grass land and cultivated land were the dominant land use types in the past two decades, aggregately accounting for over 96% of the study area. Land use transformation took place mainly in 2005-2010 and 2015-2020. It were manifested by two major forms, including the conversion of cultivated land into forest and grass land and the conversion of forest into grass land. As a result, the area of cultivated land declined by 386.62 km2 in the past two decades. In general, the land use spatial structure kept relatively stable while that of some parts of the study region demonstrated drastic change during the study periods. (2) As for landscape pattern, the landscape diversity and evenness index increased while the contagion index dropped. Specifically, the largest patch index of forest decreased while that of grass land rose. For most land use types, the patch density grew while the aggregation index fell, indicating an increasing fragmentation trend against the background of land use structure generally optimizing, especially for forest, cultivated land, and grass land. In the meantime, continuous expansion of construction land was observed. (3) In terms of landscape security pattern, the past two decades witnessed a remarkable improvement of the landscape ecological security level in the study area. The proportion of area with a security level higher than "relatively low security" surged from 62.35% in 2000 to 98.11% in 2020. As for the spatial features of landscape security pattern, the level of landscape ecological security was high in the north and low in the south initially. Thanks to relentless efforts put into rocky desertification control and ecological improvement, the security level of the south increased considerably. This consequently contributed to a relative balance of security level between the north and south of the study area. In addition, the landscape ecological security index was featured by significantly spatial agglomeration, with high-high value clustered in the north and low-low value clustered in the south. These findings underscore the need for further advanced ecological conservation to ensure the ecological barrier function in the north and further intensified ecological restoration to improve the landscape ecological security level in the south of the study area. In addition to vigorously enhancing rocky desertification control, it is also crucial to strike a balance between economic development and ecological conservation to ensure the long-term stability of local landscape ecological security.