Abstract: Based on the simulating experiments and calculated results of multivariant gas-liquid balance sitnulation,the geochemical characters and hydrocarbon-generating processcs of samples and the influnce of experimental temperature on oil-expelling efficiency were analysed.The authors recognized that oil generation was a main motive force for oil-expelling;thermal evaporation was a major factor resulting in a false apparent oil-expelling efficiency in the thermal pressure oil-expelling experiment.On this hasis,a confidence index for quantitative evaluation of experimental oil-expelling efficiency and a reasonable calculating method of apparent oil-expelling efficiency were suggested.