Abstract: The abnormal high-pressure of fluid controls the hydrocarbon-forming mechanism of source rocks and the migration and accumulation of oil and gas. Overpressure promoted the hydrocarbon generation of sulphur-rich source rocks in the upper sub-member of Es⁴; by contraries, it restrained the hydrocarbon generation of sulphur-poor source rocks in the middle and lower sub-members of Es³. Thus, in the former situation, hydrocarbon generated and discharged early, its maturity was lower, and it filled the peripheral and top traps of sags; in the latter, hydrocarbon generated and discharged late, its maturity was higher, and it filled the inner and lower traps of sags. The abnormal hygh-pressure of fluid also formed passages for hydrocarbon migration and accumulation. For the future, the forecast of subtle transportation systems is the key of exploration for lithological reservoirs.