The petroleum province, oil and gas bearing area ,of the Xujiahe formation second-third member in the north section of Longmen mount foreland basin were divided into three  parts: the Zitong sag west slop petroleum province, the Zitong sag east slop petroleum province and  the Jiulongshan petroleum province on the basis of its tectonic evolution, hydrocarbon generation history, the kinds of pore and density of microcrack in Xujiahe formation second-third member's sand bodies. The Zitong sag west slop petroleum province: 1.The Xujiahe formation second-third member's four huge overriding sand bodies are generated by quick aggradation of sediment in early-medium Norian stage; 2.The fresh water leaching during epigenesis late Norian stage results in the intragranular-intergranuler solution pore generating in these sand bodies; 3. Subsequently, the microcrack in these sand bodies grows as a result of the geostatic pressure or dynamic pressure in medium-deep buried diagentic enviroment; 4. These sand bodies and the huge ancient uplift constitute a huge ancient compound trap, which catchs oil and gas all time.