Abstract: Simulation of hydrocarbon generation and expulsion of source rock in finite space has been carried out with the hydrocarbon generation and expulsion simulation experimental instrument of type DK-Ⅱ with porosity,temperature and pressure under geological conditions.It has been concluded that the process of hydrocarbon generation of source rock during basin subsidence can be divided into 3 stages as follows.1)R_o≤0.70%,oil generates from source rock slowly;2)0.70% R_o 0.90%,oil generates rapidly,and reaches the peak when R_o is 0.90%;3)R_o 0.90%,oil gene-ration from kerogen has finished due to the fluid pressure in source rock.And during the 3rd stage,the oil expulsed from source rock cracking stays on rock surface and in connected microfractures.Part of the expulsed oil migrates into sandstones which interbed with source rocks.When the maturity of source rock is over 0.70% and the pressure differential between source rock and reservoir during basin uplifting reaches about 4-5 MPa,oil migrates far away and accumulates.