The basic data about continental oil generation is still the theory on thermal degrada-tion of kerogen commonly used in the world.But during the exploration of hydrocarbon in Jiyang Depression

it was found that the theory should be added and improved.A geo-chemical model of oil-gas generation in two stages—the early and.late stages—has been proposed in this paper.The parent materials to generate oil and gas in the early stage was hydrocarbon polymer parts with low chemical activity contained in some organisms lived in lacustrine basins such as hydrocarbon-rich Botryococcus braunii which containned more than 40% soluble hydrocarbon when cultured living body and generated saturate hydrocarbon series after thermal simulation (R

0

<

0.30%).Two stages of thermal depolymerization and thermal degradation were divided in the late stage.low-matured oil and gas were generated in thermal depolymerization

matured and high-matured oil and gas were generated in thermal degradation.The parent materials of kerogen

favourable for hydrocarbon generation were controlled by biology-rich zones

which would generate the major source beds.As there are much differences in geothermal fields

the source threshold would be controlled by sedimentary units in minor sags.