This article investigates the geological characteristics and sources of bitumen in Cambrian reservoirs of the Ordos basin. We analyzed the distribution, content, petrological characteristics, maturity, elemental composition, biomarkers, and carbon isotopes of reservoir bitumen. Our findings indicate a significant enrichment of bitumen in Cambrian reservoirs, primarily concentrated in strip- shaped and circular patterns in microcracks, intergranular and dissolution pores. Bitumen exhibits distinct boundaries, high thermal evolution evidenced by equivalent vitrinite reflectance value ranging from 1. 35% to 3. 48%, and a high carbon atom composition attributed to thermal cracking. Biomarker analysis reveals a predominance of C27 regular steranes, C23tricyclic terpenes, and phytanes, indicative of a reducing depositional environment that originated from lower algae. The high ratio of tricyclic terpenoids to hopanes and the low ratio of hopanes to steranes further support a marine origin for the bitumen.Additionally, the high triaromatic dinosteroid parameter (triaromatic dinosteroids/(303- methyl- 24- ethyl triaromatic steroids+triaromatic dinosteroids)) and (C26+C27)/C28triaromatic steroids ratio closely resemble the distribution characteristics of the Dongpo Formation source rocks. Moreover, organic carbon isotopes and similar trends in Rb/Sr, Zn/Co, and Cu/Sr ratios corroborate the conclusion that the bitumen in Cambrian reservoirs in the southern and eastern Ordos basin mainly originates from the Dongpo Formation. Consequently, these findings suggest that hydrocarbons generated from the marine source rocks of the Dongpo Formation have migrated and accumulated in the southern and eastern Ordos basin. Therefore, the Cambrian primary reservoirs in the southern Ordos basin hold significant exploration potential for hydrocarbon resources, warranting further investigation.