There are two sets of reservoirs, Oligocene Huagang oil reservoir in the upper and Eocene Pinghu gas reservoir in the lower, in Pinghu Field, East China Sea Basin. The anticline structure controlled by the large fault formed during Paleocene to Eocene and traps formed in Pinghu phase. Accompanying with Yuquan movement that happened after deposition of Pinghu Formation, deposition of Huagang Formation started during middle Miocene, meanwhile hydrocarbon expelled and immigrated from the Pinghu source rock into sandstone reservoir within Pinghu Formation, which is the first injection for liquid hydrocarbon. Accompanying with the deposition of Huagang Formation and regional tectonic movement, hydrocarbon in Pinghu sandstone reservoir migrated up partly into Huagang reservoir. From the end of Miocene till now, gas generated from source rock below Pinghu Formation, which is the secondary injection for gaseous hydrocarbon. Since gaseous hydrocarbon injected into Pinghu Formation, the liquid hydrocarbon was forced to migrate upwards to Huagang Formation and gas-dominating reservoir formed gradually. The upwards-migrating liquid hydrocarbon injected into Huagang reservoir and oil-dominating reservoir formed because of the weakening breakthrough pressure in cap rock at the top of Huagang, which resulted in escaping of gas but was favorable to preservation of oil. The large-scaled sandstone bodies with abnormal high pressure without affection of a tectonic movement are the promising oil reservoirs in deep.