Recently，Yangjiang Sag has become a new area that has made major breakthroughs in petroleum exploration in Pearl River Mouth Basin. To clarify the hydrocarbon generation potential and accumulation contribution of source rocks of Enping 21 Subsag in Yangjiang Sag，the sedimentary environment，source of organic matter，and hydrocarbon generation potential of source rocks of Wenchang Formation drilled in Yangjiang Sag were systematically analyzed，using methods combining inorganic element analysis with organic geochemical analysis in this paper. The sources of the discovered crude oil were identified and the accumulation contribution of source rocks in different sedimentary environments was estimated. The results show that Enping 21 Subsag is characterized by a humid-hot climate，and a deep freshwater lake basin with low salinity in a sub-reductive environment on the whole，and two sets of high-quality source rocks，including semi-deep to deep and shallow to semi-deep lacustrine source rocks，are developed during the deposition of Wenchang Formation. The oilsource correlation and the calculation of the proportion of crude oil from different sources in the reservoirs indicate that the crude oil from shallow to semi-deep lacustrine source rocks accounts for 85%，and that from semi-deep to deep source rocks only accounts for 15%. The shallow to semi-deep lacustrine source rocks also have strong hydrocarbon supply ability，and the shallow and small subsags developed with shallow to semi-deep lacustrine source rocks also have great petroleum resource potential.