Abstract: The Weixinan Sag in the Beibu Gulf Basin of the South China Sea is a hydrocarbon-rich sag. However, currently limited oil and gas were found in the 2nd member of Weizhou Formation, and the hydrocarbon accumulation characteristics and laws were unclear, which restricted next exploration direction. The main controlling factors and accumulation rules of oil and gas in the 2nd member of Weizhou Formation were studied based on laboratory tests and drilling and seismic data. The crude oil of Weizhou Formation was mainly originated from the thick oil shale in the central and upper parts of the 2nd member of Liushagang Formation. The lacustrine mudstones in the upper part of the 2nd member of Weizhou Formation provided regional cap rocks. Oil and gas were mainly distributed close to the source rock connected faults of the no.2 fault zone, which were the keys for hydrocarbon accumulation. Fault block traps with roof ridge structures generated by reverse faults and SGR>0.64 and SSF<1.70 at fault sections were favorable for hydrocarbon accumulation, providing an exploration target and direction for the next step.