Abstract: A breakthrough in natural gas exploration has been made in well Yican 1 of Southeastern Ordos Basin, while the hydrocarbon potential of its source rocks hasn’t been studied. Several source rock samples collected from Shanxi and Majiagou Formation were used for relative study. The results show that the TOC content of four mudstone samples from Shanxi Formation varies from 0.54% to 2.31%, with the average content of 1.65%. (S₁+S₂) value varies from 0.12 mg/g to 0.46 mg/g, with the average value of 0.34 mg/g. Shanxi Formation mudstone source rocks have a high abundance of organic matter and strong hydrocarbon generation potential. The TOC content of dolomitic (calcareous) mudstones from Majiagou Formation varies from 0.09% to 0.33%, with the average content of 0.17%. (S₁+S₂) value varies from 0.03 mg/g to 0.17mg/g, with the average value of 0.12mg/g, which is evaluated to be poor to non-hydrocarbon source rocks. The compositions of carbon isotope in CH₄ and C₂H₆ were compared, and the results show that well Yican 1 has the characteristic of δ¹³C₁>δ¹³C₂, which indicates that the natural gas is mainly coal type gas mixed by a small amount of oil type gas. And the coal type gas is mainly from the coal layers of Upper Paleozoic, whereas the oil type gas is mainly from premium marine facies source rocks of Taiyuan Formation in Upper Paleozoic. The investigation of the hydrocarbon potential and gas genesis of Ordovician Majiagou Formation is favorable to study its gas generation and formation characteristics, and it is of great significance to the study of gas field formation model, resource prospects and exploration.