The comprehensive studies on the sedimentary settings in Jungar and Tarim Basins shown clearly that China’s northwestern was mainly sedimentary marine environments and the basements of sedimentary basins were a number of separated ancient crystalline massifs covered by sea water,among which there were palaeo-ocean trough or/and narrow palaeo-ocean trough.The marginal basins along the trough between different massifs or the marginal zone between massif and ocean trough are favorable for oil and gas generation. During the processes of mountain-building with the compressional folding to the ocean trough,the ancient system of MassifTrough transformed from the Palaeozoic marine environments to the Meso-Cenozoic continental sedimentary system of Mountain-Basin, during which time the ancient series of marine source rocks deposited in the marginal basins were bund under the mountains around the basins. And the oil and gas generated from the source rocks have been partly migrated and accumulated into reservoir beds in the basins, which consists of the oil and gas accumulation type so-called"out-generating and inner-reservoiring". Within this kind of basins, there coexist of two series of source rocks: marine one and continental one, and two kinds of combination complexes of petroleum generating and reservoiring: "inner generating-inner reservoiring" and "out generating-inner reservoiring". This new theory or model of petroleum formation and occurrences has been proved not only by the result of our recent petroleum geochemical research but also by the practice of exploration in some regions. The new conception about petroleum generation from Massif-Trough’s marginal zone has been out of the traditional concepts to study on the formation and occurrence of the Palaeozoic petroleum limited by the modern basins, which could be to increase potential petroleum resources discovered and to enlarge new fields for finding oils and gases in Northwest China so that the highly meaningful importance should be come out.