Abstract: Hydrocarbon generation potential of source rocks decreases when some hydrocarbon is expulsed.Upon this principle,the process of hydrocarbon expulsion can be simulated.This study utilizes characteristics of variation of hydrocarbon generation potential index (S₁+S₂)/TOC during burial,to determine expulsive threshold of source rocks.Its expulsive ratio,expulsive rate and expulsive efficiency can also be determined.Because difference of hydrocarbon generation potential index between different types of source rocks is significant,each type of source rock should be simulated respectively.The approach is applied to model the characteristics of hydrocarbon of the Lower Tertiary source rocks in the Jiyang Depression.Results show that,characteristics of hydrocarbon expulsion of oil shale is different from that of dark mudstone.Expulsive threshold of oil shale is shallower than that of dark mud,and its expulsive rate is also higher than that of dark mudstone.