Abstract: The Donghetang Formation in the Bashituo area of the Tarim Basin is dominated by an open shoreline depositional system, characterized by horizontally continuous sandbodies with substantial vertical thickness. Exploration practices have confirmed its favorable hydrocarbon potential; however, the lack of detailed understanding of sandbody sedimentary genesis currently limits the prediction accuracy of favorable reservoirs. Based on core data, experimental results, logging data, and 3D seismic data, this study employs detailed descriptions of core lithofacies, sedimentary structures, and cyclic sequences, combined with grain size analysis, logging facies association classification, and post-stack reconstructed acoustic impedance inversion techniques. The objectives are to determine the affiliation of sedimentary subfacies belts and microfacies types in the study area, characterize the spatial evolution of sedimentary microfacies, and summarize the main controlling factors of sedimentation. The results indicate that: ① The sandbodies of the 4th to 6th sand groups in the lower sandstone member of the Donghetang Formation belong to foreshore deposits, which can be divided into four microfacies types: foreshore bar microfacies (dominated by massive and rhythmic bedded coarse sandstone and pebbly coarse sandstone), bar margin microfacies (dominated by parallel bedded and rhythmic bedded medium sandstone, with interbedded thin-bedded coarse sandstone), sheet-like shoal microfacies (dominated by massive and cross-laminated fine sandstone), and inter-bar bay microfacies (dominated by horizontally bedded, cross-laminated, and massive fine-grained sandstone and mudstone); ② From the 4th to the 6th sand group, the foreshore bars migrated continuously seaward spatially, and the vertical sequence is dominated by retrogradational cycles. The sandbodies at the top of the 6th sand group are predominantly coarse-grained foreshore bar deposits; ③ The spatiotemporal evolution of each microfacies is controlled by two key factors: first, the large-scale regression during the sedimentary period of the study interval, which drove the continuous seaward progradation of foreshore bars and increased the proportion of coarse clastic components in the study area; second, the multi-level slopes in the shoreline zone controlled the formation of breaker zones and constrained the spatial distribution of foreshore bars. Under the combined constraints of sea-level fluctuations and multi-level shoreline slopes, the Bashituo area is endowed with widely distributed thick-bedded foreshore sandbodies, laying a material foundation for hydrocarbon accumulation. The determination of sedimentary subfacies belts, microfacies types, and the clarification of spatiotemporal evolution laws and main controlling factors provide a theoretical reference for the sedimentary analysis of the "Donghe Sandstone" in this area and even the entire Tarim Basin.