Based on the experiment of total organic carbon (TOC), rock pyrolysis, extractable organic matter, and gas chromatography-mass spectrometry (GC-MS), 4 sets of hydrocarbon source rock samples of the third member of the Shahejie Formation (Es3) of the Bozhong sub-basin, Bohai Bay Basin, Northern China, have been tested. The data of TOC and extractable organic material (EOM) content show that the abundance of organic matter of Es3 reached a good-excellent level. The data of kerogen macerals and Tmax and HI both indicate that the organic matter type was mainly type II, with a small amount of types I and III. The vitrinite reflectance (Ro), Tmax, and methylphenanthrene index (MPI) all show that the maturity of the source rocks of Es3 increased gradually with increasing depth and generally at the low mature-mature stage. The depositional setting was dominated by a transitional oxidation-reduction environment with partial salinization. The salinization of aquatic bodies was conducive to the formation of a good reducing environment. The parent material source of the organic matter in the source rocks of Es3 was dominated by algae and mixed with other lower aquatic organisms and higher plants.