Recently, increasing numbers of oil and gas reservoirs have been discovered in the Wenchang Depression, western Pearl River Mouth Basin, South China Sea, revealing prospects for hydrocarbon exploration. The Enping Formation (E₃e) is a key target layer for the development of source rocks. However, previous work has only focused on lacustrine swamp source rocks of E₃e in the Wenchang A Sag, without a systematic study of shallow lacustrine source rocks. In this study, the quality of E₃e shallow lacustrine source rocks is reevaluated, and the hydrocarbon generation and expulsion characteristics are analyzed using relevant geological data and constructing a conceptual model. The results show that the E₃e₂ source rocks have greater thickness (50–600 m) and similar organic matter abundance (0.5–2.5%) compared with the E₃e₁ source rocks (50–500 m and 0.5–2.5%). On the whole, the E₃e source rocks were deposited in the continental environment and are dominated by Type II and Type III kerogen. Meanwhile, the E₃e source rocks of the Wenchang A Sag are in the stage of mature to over mature, while those of the Wenchang B Sag are in the stage of low mature. Vertically, the hydrocarbon generation potential of the E₃e₂ source rocks is greater than E₃e₁. Also, the cumulative hydrocarbon production of steep slope in the Wenchang A Sag is larger than that in the Wenchang B Sag. In addition, the corresponding vitrinite reflectances of hydrocarbon expulsion threshold and peak are 0.72 and 0.96%, respectively. Horizontally, four hydrocarbon generation and expulsion centers were mainly concentrated in different subsags of the Wenchang A and B Sags for E₃e. The maximum values of hydrocarbon generation and expulsion intensity for E₃e₁ are 1500 × 10⁴ t/km² and 1000 × 10⁴ t/km², respectively, while those for E₃e₂ are 1800 × 10⁴ t/km² and 1200 × 10⁴ t/km², respectively, with the expulsion efficiency of 75%.