The late Carnian to early Norian (Late Triassic) represents a critical interval of climate reorganization from humid greenhouse to more arid regimes with significant impacts on terrestrial and marine ecosystem evolution. This study provides a comprehensive qualitative and quantitative palynological investigation of the Carnian-Norian boundary at the Guanyin Ya (HWG) in the western Sichuan Basin to establish a palynostratigraphic framework, reconstruct floristic composition and vegetation dynamics, climate evolution, and depositional conditions in a foreland basin setting. The new palynostratigraphic constraints refined the age of the upper Ma'antang and Xiaotangzi deposits spanning from the late Carnian (late Tuvalian) to early Norian (Lacian) based on age-diagnostic palynomorphs, including the first appearance of Ricciisporites tuberculatus, Classopollis torosus, Samaropollenites speciosus, Quadraeculina anellaeformis, and Chasmatosporites hians and the last occurrence of Aulisporites astigmosus and Pseudoenzonalasporites summus. Across the Carnian-Norian transition, the palynofloral assemblages are marked by a progressive increase in xerophytic conifers relative to a decline in hygrophytic and mesophytic fern spores, lycopsids, mosses, cycadophytes, and bennettites. Such palynofloral changes reflect the development of a mixed forest ecosystem and a shift from semi-humid and warm climate during the late Carnian to seasonally dry monsoon-influenced arid to semi-arid climatic regimes during the early Norian. This pattern coincides with coeval records from the Tethyan and Boreal realms, where humid lowland vegetation declined compared to the widespread expansion of xerophytic palynoflora. This trend implies the combined interaction between global climates and regional controls, governed by paleolatitudinal gradients and the northward migration of the Intertropical Convergence Zone, which modulated seasonality, precipitation, and moisture regimes during the Late Triassic. Palynological data further indicated strong terrestrial input from adjacent hinterlands and deposition in a marginal to shallow marine foreland basin within the tectonically subsiding foredeep western Sichuan Basin influenced by eustatic sea-level rise. This reflects the coupled impact of eustatic sea-level, regional tectonics, and basin evolution in controlling paleoenvironments and palynofloral communities in the eastern Paleo-Tethys Ocean during the Late Triassic.