Abstract: The potential of oil generation and expulsion within the oil-window of coal as a kind of source rocks with high rich-organic matter is controversial for a long time. Study on the simulation of hydrocarbon generation and expul- sion for an immature typical brown coal with transitional organic matter type Ⅱ2 -Ⅲ in confined system,under the con- ditions of water existing,different temperature,overburden and internal fluid pressure,was carried out,using DK-Ⅱ hydrocarbon generation and expulsion simulation experimental instrument. The results of simulation experiment show that coal mainly generates oil at each evolution stage of the maturity Ro≤0. 82% ,and the yield of generation oil is ob- vious higher than the yield of generation hydrocarbon gas,the main oil generation stage of coal is at 0． 68 ≤Ro ≤ 0． 82% ,the percentage of episodic quantity of generated oil to total oil is 53. 66% ;and coal mainly generates hydro- carbon gas at each evolution stage of the maturity Ro >0. 82% . Coal not only can generate oil,but also can expel oil with high efficiency when the oil yield reaches about 30 mg / g TOC,the percentage of expulsion oil of coal is obvious higher than the percentage of expulsion of mudstone within main oil-window. The yields of hydrocarbon gas and CO2 of coal is obvious higher than the yields of hydrocarbon gas and CO2 of mudstone within main oil-window. This may be an important factor causing coal with higher expulsion oil efficiency.