By establishing functional relation between shale gouge ratio (SGR) value of fault zone and the height of oil column laterally sealed by fault, the discussion on quantitative evaluation method of fault lateral seal ability is carried out and the lateral seal ability of faults in Beier Depression is studied quantitatively. The results show that SGR value of fault zone has exponential relation with oil column height which is sealed by it, and fault lateral seal ability depends on 3-dimension distribution of SGR value of fault plane.