Abstract: From a perspective of production-living-ecological (PLE) space, a functional space evaluation system of “production suitability, living suitability, and ecological importance” was constructed to understand the spatial pattern and evolution characteristics of the PLE function of Bailongjiang Watershed in southern Gansu from 1990 to 2014. The results showed that: (1) The strong production functional spaces (SPFS) were mainly distributed in Tanchang-Zhouqu-Wudu section along both bank areas of Bailongjiang, both bank areas of Baishuijiang, and the central and eastern parts of Wenxian, which were characterized with high population density. They were roughly bounded by the Tanchang-Zhouqu-Wudu section of Bailongjiang, with the eastern parts being the semi-productive functional space (S-PFS) and the western being the weak production functional space (WPFS). The areas of the SPFS and S-PFS were shrunk by 2434.54 and 294.07 km² respectively, while WPFS was expanded by 2728.62 km². The pattern was relatively fragmented during 1990-2002, with no obvious patch gathering areas. The strengthened areas were concentrated in the northwestern part of Diebu during 2002-2014, while the weakened areas were located in the middle and lower reaches of the watershed. (2) The spatial pattern of the living functional space was similar to that of the functional space for production. The area of the strong living functional space was increased by 119.32 km². With some fluctuations, the half living functional space was reduced by 508.23 km² and the weak living functional space was increased by 388.90 km². The changes of such pattern were mainly concentrated in the Tanchang-Zhouqu-Wudu section of both bank areas of Bailongjiang and the most area of Wenxian, being strengthened in 1990-2002, but weak in 2002-2014. (3) The ecological functional space was the strongest in the northwestern and southeastern parts, followed by middle part, and the weakest in west part of the watershed. The area of the strong ecological function space was increased by 3118.13 km² after a sharp drop. The area of the semi-ecological function space was decreased by 508.23 km². The area of the weak ecological function space was decreased by 1566.08 km² in fluctuation. During 1990-2002, the strengthened areas were mainly located in the northwest corner of the watershed, and the weakened zones were concentrated in the junctional zones between Zhouqu and Diebu and between Zhouqu and Wudu, southern Wudu, and southwestern Wenxian. During 2002-2014, the function was degenerated in the northwest corner of the watershed, and improved in the junctional area of Diebu and Zhouqu, and the southeastern Wudu. (4) The changes of land use pattern and ecosystem services caused by deforestation and the project of returning farmland to forest and grassland were the major causes for the changes of spatial pattern of PLE space. Our results provided reference for the identification of PLE functional space in similar mountainous watersheds.