Abstract: The Songliao basin, China’s largest northeastern sedimentary basin, is a key uranium basin with unique sandstone-type uranium-hosting conditions. To clarify the uranium-mineralization regularities in the southern part of the basin and locate favorable mineralized layers, the source characteristics of uranium in the uranium-bearing red heterogeneous layers and their connection to uranium mineralization were focused on in this study. Field and core observations, along with detrital zircon U-Pb dating, were carried out. The gravel distribution of the red heterogeneous layers and the age distribution of detrital zircons were analyzed. During the deposition of the Quantou formation, the main source was the Zhangguangcailing in the southeastern part of the basin, while a secondary source was identified as the Kangping-Faku Hills in the south. In the case of the Qingshankou formation, three provenance systems were recognized: The principal one originated from the Kangping-Faku Hills, the central part was supplied by the Jiamatu Uplift, and the northern Tongyu area was sourced from the southern segment of the Greater Khingan Range. From the deposition of the Quantou formation through that of Qingshankou formation to the Yaojia formation, the provenance system was gradually shifted westward, starting from the Zhangguangcailing, moving towards the Kangping-Faku Hills, and finally reaching the southern Greater Khingan Range. Detrital zircon U-Pb dating of nine samples shows that detrital sediments in the red heterogeneous layers originate mainly from three directions: southeast, south, and northwest. Southeastern geological bodies are predominantly Permian and Triassic granites, southern ones are Early Cretaceous intermediate-acidic volcanic rocksm, and northwestern ones are Jurassic volcaniclastic rocks from the Greater Khingan Range. During deposition of the Quantou formation, uranium-rich lithologies are mainly Early Cretaceous intermediate-acidic volcaniclastic rocks and Permian granites, with a small amount of Late Paleozoic metasedimentary rocks. For the Qingshankou formation, they are primarily Late Jurassic—Early Cretaceous intermediate-acidic volcaniclastic rocks and Permian—Triassic granites. For the Yaojia formation, they consist mainly of Late Jurassic—Early Cretaceous intermediate-acidic volcaniclastic rocks, with a small amount of Permian–Triassic granites. Detailed analysis of provenance-uranium source characteristics in the southern Songliao basin reveal that uranium mineralization shifts westward continuously. This shift is closely linked to the sedimentary-subsidence center, provenance system, and westward-migrating fluvial sand bodies. Key mineralization layers progress from the southeastern basin (Quantou formation) to the central area (Qingshankou and Yaojia formations) and then to the western region (Nenjiang, Sifangtai, and Mingshui formations). Overall, the provenance-uranium source system controlled by the Kangping-Faku area is more favorable for uranium enrichment. Thus, the Qingshankou and Yaojia formations are identified as the primary targets for sandstone-type uranium exploration in the study area.