Abstract: Sporopollen fossils play an important role in stratigraphy division and correlation, vegetation succession, and paleoclimate reconstruction. This study focuses on Liushagang Formation in the Weixi’nan sag of Beibuwan Basin, where palynological analysis was conducted to quantitively reconstruct the paleoclimate during its depositional period. The research results are as follows. (1) The sporopollen assemblage is mainly dominated by angiosperm pollen, with notable abundances of Quercoidites and Cupuliferoipollenites. Besides, the gymnosperm pollen is primarily represented by Abietineaepollenites and Piceaepollenites, while the fern spores are dominated by Polypodiaceaesporites. (2) Based on variations in sporopollen content and species composition, three sporopollen assemblages have been identified in Liushagang Formation, including Assemblage Ⅰ (Polypodiaceaesporites-Cupuliferoipollenites-Osmundacidites) in the middle-lower part of the third Member of Liushagang Formation, Assemblage Ⅱ (Quercoidites-Ulmipollenites-Pentapollenites) in the upper part of the third Member of Liushagang Formation to the upper part of the second Member of Liushagang Formation, and Assemblage Ⅲ (Leiosphaeridia-Granodiscus) in the top of the second Member of Liushagang Formation to the lower part of the first Member of Liushagang Formation. (3) Through analyzing the vegetation, humidity, and climate types of the nearest living relatives of sporopollen fossils, the vegetation and paleoclimate for each assemblage were quantitatively reconstructed. During the development of Assemblage Ⅰ, vegetation was dominated by deciduous and evergreen broad-leaved trees, with well-developed herbaceous plants. The content of mesophytic sporopollen was the lowest among the three assemblages, while that of helophytic and hygrophytic sporopollen is the highest, indicating a semi-humid subtropical climate. During the development of Assemblage Ⅱ, herbaceous plants declined, conifers and evergreen broad-leaved trees increased, mesophytic sporopollen rose, and helophytic types decreased, reflecting a semi-humid to semi-arid central subtropical climate. During the development of Assemblage Ⅲ, the evergreen broad-leaved trees continued to develop, and the content of mesophytic sporopollen further increased, indicating a sustained semi-humid to semi-arid subtropical climate. (4) Quantitative paleoclimate reconstruction using the coexistence approach reveals that during the deposition of Liushagang Formation, the mean annual temperature (MAT) ranged from 13.3 ℃ to 19.8 ℃, the warmest month mean temperature from 25.8 ℃ to 27.5 ℃, and the coldest month mean temperature from 1.9 ℃ to 11.9 ℃. Moreover, the mean annual precipitation (MAP) ranged between 797.5 mm and 1 113.2 mm, and the average maximum and minimum monthly precipitation ranged from 179 4 mm to 239.1 mm and from 10.2 mm to 11.3 mm, respectively. Climatic fluctuations occurred within the depositional period, with an overall trend of decreasing MAT and MAP from the third Member to the first Member of Liushagang Formation.