Provenance analysis is of great significance in determining the sediment source, parent rock properties, sediment transport distance, and even sedimentation and tectonic evolution of the whole basin. Heavy mineral assemblages, light mineral assemblages, REE distribution pattern and palaeocurrent direction were systemically analyzed in this paper. Six main provenances in the Oligocene period of western Qaidam Basin were determined, i.e., eastern Altun provenance, western Altun provenance, Aral provenance, Tomorlog provenance, Qimantag-Dongqaishan provenance, and Wanxi-Gansen provenance. Provenance characteristics significantly control sediment characteristics.