Abstract: By means of cores observation and analysis of imaging welllogging data, it shows that vertical fractures were developed in Budate Group of Beier depression. The formation and distribution of vertical fractures were controlled by the faults. By the vitrinite reflectance required in deposition of silica or carbonate, the vertical seal of vertical fractures in Budate Group of Beier depression now was studied. It shows that vertical fractures are open in most of the area, and closed only in a few areas of the depression. Sealed areas distributed in stripe on the edge of the depression and in ring in the centre of the depression. The vertical sealing ability of the vertical fractures in Budate Group of Beier depression in geohistorical periods is better than that of the present. Oil & gas preservation conditions become worse and worse, a great deal of oil-gas has been lost in the past.

Key words: Beier depression, Budate Group, vertical fractures, vertical seal, evolution characteristion, vitrinite reflectance