Controlled by deposition process and tectonic evolution，different pressure systems generated vertically in the faulted basins. Hydrocarbon accumulation conditions in normal and in abnormal pressure systems are different，resulting in different oil and gas accumulation models and distributions. In order to ascertain the pressure distribution and reservoir forming characteristics in faulted basins，the Palaeogene series in Gunan subsag was studied in detail as an example. According to the measured and calculated data，it is known that normal pressure system with pressure coefficient less than 1.2 exists in Palaeogene formations shallower than 3 000 meter（including Es2 and the strata above）in Gunan subsag，and high pressure system with pressure coefficient more than 1.2 in exists in the formations deeper than 3 000 meter（strata below Es3）. According to formation pressure and hydrocarbon distribution，two hydrocarbon accumulation systems，one with normal pressure outside the source rock and the other with abnormal pressure inside the source rock，were identified in the Palaeogene in Gunan subsag. The hydrocarbon accumulation system with normal pressure outside the source rock is above the source rocks mainly developing tectonic traps in faulted blocks，where hydrocarbons generated from the middle and the lower segments of Es3 migrated vertically into Es2 and the formations above through faults outside the source rocks，or directly migrated into the faulted blocks and rollover anticlines to accumulate，or laterally migrated into appropriate traps to accumulate. The hydrocarbons are entrapped in the fault zones near the source. The hydrocarbon accumulation system with abnormal pressure exists in the source rocks with dominant lithologic or structural-lithologic traps，where hydrocarbons were driven by the high pressure in the source rock and migrated laterally into the adjacent sand bodies or structural-lithologic traps to accumulate. The oil-bearing reservoir distribution is controlled by pressure and lithologic bodies.