Abstract: Geochemical characteristics of hydrocarbon in reservoir are not only controlled by the organic-phase，maturity and sedimentary environment of source rock，but also affected by many other geological and geochemical factors including biodegradation，water washing ，fluid/rock interaction and geochromatography(during hydrocarbon migration and accumulation)，phase-controlling molecular fractionation (during hydrocarbon migration and entrapment)。thermal alteration，multiple charge and mixed of petroleum，dissemination(reservoir overprinting ，solubilization)and thermochemistry sulfate reduction，etc．，during petroleum migration and accumulation．In this paper，the influences of the geological and geochemical factors on the geochemical characteristics of petroleum ， such as biodegradation an d water washing ，fluid／rock interaction and geochromatography，phase-controlling molecular fractionation，thermal alteration，multiple charge and mixed of petroleum，dissemination and thermochemical sulfate reduction。etc．are disccessed．