Abstract: The Qilian-Altun Mountains region occupies a distinctive biogeographic position and supports substantial plant diversity, making characterization of the regional flora important for biodiversity conservation and sustainable resource management. In the present study, seed plant diversity and floristic composition were evaluated through field surveys and systematic compilation of existing records. A total of 645 seed plant species representing 63 families and 281 genera were recorded. Angiosperms dominated the flora, comprising 639 species in 277 genera and 60 families, with dicotyledons representing 81% of the angiosperm flora. Floristic composition showed considerable geographic complexity and multiple biogeographic affinities. At the family level, cosmopolitan and pantropical elements were predominant, whereas genera were characterized mainly by north temperate distributions. Most floristic elements showed strong associations with the Qinghai-Xizang Plateau. Dominant genera also exhibited pronounced north temperate affinities, indicating a clear temperate character of the regional flora. Overall, these distribution patterns reflect the location of the Qilian-Altun Mountains region within a climatic transition from the warm-temperate zone to the temperate zone and highlight the combined influence of regional climate and biogeographic history on seed plant diversity.