Abstract: Grain size in aeolian sediments is fundamental to studying geomorphic evolution, arising from interactions among fluvial deposits, sediment sources and aeolian airflow. Analyzing grain size characteristics helps to understand sediment transport processes, improve wind erosion mitigation techniques, and explain geomorphic development. Previous studies on grain size in the Taklamakan Sand Sea of China have mainly focused on individual dunes, overlooking variations among different dune types. Although spatial patterns of grain size parameters are well-documented in other Chinese deserts, they remain poorly understood in the Taklamakan. To address this gap, 700 surface sediment samples were collected from the Taklamakan Sand Sea, including transverse dunes, linear dunes, pyramid dunes, reticulate dunes, vegetated dunes and interdune areas, to characterize grain size distribution across dune types and the sand sea. The Taklamakan Sand Sea is dominated by fine sand (125–250 µm) and very fine sand (63–125 µm), with minimal proportions of coarse sand and larger fractions, suggesting that sand transport predominantly occurs through saltation. Grain size characteristics differ significantly among dune types, indicating that grain size characteristics may be a dune classification index in geomorphology. The significant correlation between the grain size characteristics of transverse dunes and linear dunes suggests a possible transformation relationship between these dune types in the Taklamakan Sand Sea. Spatial variations in grain size are controlled by dune type, local geomorphology, and wind regimes. Higher wind speed in the east caused the mean grain size of aeolian sands to decrease from east to west along the northeast wind. Sand sorting decreases from east to west and then increases, whereas skewness and kurtosis show no clear spatial trends. Overall, distinct grain size variations among dune types reveal previously unrecognized evolutionary connections between aeolian landforms. The spatial distribution of grain size parameters clarifies sediment provenance and transport processes in the Taklamakan Sand Sea.