Abstract: Petroleum distribution in carbonate reservoirs of Ordovician in northern slope of Tazhong area are affected by N-E strike?slip fault, and the hydrocarbon enrichment is controlled by the fault throw. But the fault throw is difficult to calculate due to deep?buried reservoir, low resolution and signal to noise ratio of 3D seismic profiles describing the reservoirs distribution as well as the too?small horizontal fault throw and the varied vertical fault throw of this strike?slip fault. The further analysis of the 3D seismic data shows that the strike?slip fault was of the feature of N-W extension and formed extensional?apart regions with different widths along the fault strike. A method is then proposed in this paper for calculating the strike?slip fault width and height of extensional?apart regions to indirectly recognize and determine the fault throws. The results indicate that this method can be used to recognize the hydrocarbon distribution in this area, because of its high agreement to the strike?slip fault development regularity and good coincidence to the oil?gas distribution in this area