Abstract: In the light of the model of oil-gas primary migration proposed by Di-ckie and Zhen Bing Qinru,on the basis of the study on claystone compa-ction in Jianghan Basin,the authors have suggested a formula for the cal-culation of hydrocarbon expulsion quantity.Q=w.q.d,using relative permeability of oil-gas,and the relation of oil-gas saturation to Darcy law.In selecting parameters,compaction curve of claystone in the region was ado-pted directly to calculate the quantity of interstitial fluid loss,meanwhile,with rating curve for oil-gas saturation versus relative permeability of oil-gas in the studied area,the ratios of relative permeabilities of oil-gas for the claystone under different saturations were calculated.