Urban-rural-natural (U-R-N) gradients can integrate numerous landscapes with distinct regional functions to illustrate the uncertainty, dynamics, and gradients of the mountainous socio-ecological systems. Hence, identifying transitional zones (TZs) along U-R-N landscape gradients, which contain cohesively various landscapes, and analyzing their transition trends and patterns are of paramount significance for regional landscape planning. Through the integration of geographically weighted principal component analysis (GWPCA), raster rearrangement, and abrupt bin detection, this study aims to develop a novel framework approach for identifying TZs and analyzing transition trends and type patterns along U-R-N gradients in southwestern mountains, China. The findings indicate that TZs cover 61,880 km² and account for 5.37% of southwestern mountains, primarily in the hills and mountains of the Sichuan Basin and the Yunnan-Guizhou Plateau. TZs are typically found along U-R-N gradients; however, they are most concentrated in the R1 and R2 of rural landscapes, with farmlands being the most extensively distributed land use type inside TZs. In the southwest mountains, the TZs patterns along U-R-N gradients cover 9 landscape types, including 4 TZ types, of which urban-rural transition zones (U-RTZ) account for 49.36% of all TZs and comprise the most complete U-R-N gradients. Gradients may also be detected in the component structures of TZs, and TZs have become increasingly sharp and prominent along U-R-N and topographical gradients. This framework approach overcomes the restrictions of previous TZs that were limited to nearby geographical boundaries, and can contribute to our understanding the mutual feedbacks and interactive processes of mountainous coupled socio-ecological systems, thus empowering the provision of a more elastic space for revolutionary growth while still protecting variegated natural habitats in mountains for future generations.