Abstract: In order to achieve the “oil exploration in the deep subsag” in Qikou Sag and find a new field for increasing reserves and production, Well Haitan 1 has been deployed in the deep subsag in Binhai Slope in Qikou Sag and a major breakthrough has been made. Based on the drilling results, the detailed analysis on the control mechanism of sand body development, reservoir characteristics, hydrocarbon generation conditions and hydrocarbon accumulation pattern in Dongying Formation in the deep subsag area in Binhai Slope is conducted. The study results show that: (1) The gravity flow sand body supplied by the north Yanshan provenance was developed in the third member of Dongying Formation (Dong 3 member) in the deep subsag area in Binhai Slope, showing good reservoir physical property; (2) The self-generation and self-storage oil and gas bearing system was discovered in Dong 3 member for the first time, breaking through the previous understanding of hydrocarbon migration through faults and “lower source rock and upper reservoir”; (3) The hydrocarbon accumulation pattern of “long distance sand transportation, near source hydrocarbon charging, coupling of source rock and reservoir, and contiguous oil bearing” in Dong 3 member in the deep subsag area has been established; (4) In addition, shale oil in Dong 3 member in the deep subsag area shows huge resource potential. The successful drilling of Well Haitan 1 supports to find a new field in the eastern mature oilfields and provides favorable reference for “oil exploration in the deep subsag”.