The enrichment of organic matter in sedimentary basins is the essential process of hydrocarbon source rock deposition, and the paleoproductivity is the most important factor to control this process. The Wenchang Sag is one of the main hydrocarbon- generating sags in the Pearl River Mouth Basin. A lot of researches have been carried out in the Wenchang Sag, including the distribution of hydrocarbon source rocks, the abundance, type, and maturity of organic matter, and the hydrocarbon- generating potential, etc. However, the researches on paleoproductivity and organic matter enrichment mechanism need to be strengthened sequentially. Therefore, in this paper the composition and distribution of paleoproductivity during the sedimentary period of hydrocarbon source rock in the Wenchang Sag were analyzed to provide support for the followed study of organic matter enrichment mechanism. Methods: The analysis of TOC content and rock pyrolysis was conducted using a CS- 230 carbon—sulfur analyzer in The Key Laboratory of the Ministry of Education of Terrestrial Shale Oil and Gas Formation and Efficient Development, Northeast Petroleum University. The analysis of major and trace element contents was carried out in Suzhou Sike Geological Exploration Technology Service Co. , LTD. The samples were analyzed for major element concentrations by a Axios mAX X- ray fluorescence (XRF) spectrometer. The samples were analyzed for trace element concentrations by a NexION 300D inductively coupled plasma mass spectrometry. Further details are described by Ma Pengfei et al. (2015) and Gao Ping et al. (2015). The analysis of kerogen macerals and saturated hydrocarbon GC- MS were conducted at The Analysis and Testing Center of CNOOC Zhanjiang Branch Company. The instrument used for the saturated hydrocarbon GC- MS analysis was an Agilent 5977B chromatography mass spectrometer. Results: The macerals of kerogen in the source rocks from the 2nd Member of Wenchang Formation (E1w2) are mainly composed of sapropelic group. While the macerals of kerogen in the source rocks from the 1st Member of Enping Formation (E1e1) are mainly composed of vitrinite and inertinite. The distribution of n- alkanes is mainly front unimodal or bimodal in the E1w2 source rock, and it is mainly post unimodal or bimodal in the E1e1 source rock. The distribution of C27—C29 regular steranes shows a “V” shape in the Wenchang Sag. The average ratio of (W+T)/C30H in E1w2 and E1e1 source rocks is 0. 38 and 2. 03, respectively. Conclusion: Organic matter in the E1w2 and E1e1 source rocks of the Wenchang Sag are both mixed sources. The aquatic organism in the E1w2 source rock has a greater contribution, with a higher proportion of in- situ organic matter. While the terrestrial higher plant in E1e1 source rock has a greater contribution. The E1e1 source rock has a higher total productivity index whose distribution has strong heterogeneity. During the sedimentary period of the E1e1 source rock, the total productivity index in the northern gentle slope zone is lower than that in the southern steep slope zone, and the high value of the total productivity index is mainly distributed in the places of provenance input and the central areas of the basin.