In the three cratonic basins of China, ancient source rocks are widely distributed, and understanding the mechanisms of hydrocarbon enrichment in Mesoproterozoic to early Cambrian source rocks has significant implications for ultradeep oil and gas exploration in China. This article provides a systematic summary of the source rocks in the Mesoproterozoic Chuanlinggou Formation of the North China Craton, the Neoproterozoic Doushantuo Formation of the Yangtze Craton, and the early Cambrian Yurtus Formation of the Tarim Craton. The formation processes of organic-rich shales are analyzed from the perspectives of sedimentary filling, paleoclimate, paleoenvironment, and specific geological events. It is concluded that the source rocks of the Chuanlinggou Formation developed mainly in Chuanlinggou Member 3, which experienced inner shelf sedimentation. A warm and humid climate, upwelling currents, and volcanic activity promoted nutrient input, triggered high primary productivity, and led to organic matter enrichment. Ferruginous seawater facilitated organic matter preservation. In the Doushantuo Formation of the Chuanbei depression, organic-rich intervals occur in Doushantuo Member 3. Under a warm climate, intense weathering resulting from the amalgamation of the Gondwana supercontinent promoted nutrient input and bottom-water anoxia, leading to organic matter enrichment. In the Yuertusi Formation, the enrichment of organic matter is attributed primarily to the extremely high productivity caused by intense upwelling currents and the oxygen-depleted environment resulting from transgression.