Abstract: By analysis of oil physical properties and organic geochemical features of the Permian System in the 5th and 8th districts,northwestern margin of Jungar basin, the authors come to a conclusion that the initial oil pools here were formed in an earlierstage, and afterwards they were viscosified and destroyed. At the middle and later stages the oil pools were formed again and preserved. The total organic geochemical characteristics of different generations of oil were similar and mainly originated from the Fengcheng Formation. Because of difference of reservoir formation times and secondary recreation roles, the crude oil can be divided into A1 and A2 types. The type A1 oil is of limited distribution. It was generated, migrated and accumulated in the earlier stage, and the oil pool formation time was early too. Afterwards, the oil pools were destroyed, and the crude oil was biodegradated and experienced water washing and oxidation, and therefore its density and viscosity are higher. The type A1 crude oil pools were formed in the middle to late Hercynian time, and its densification time was chiefly in the late Hercynian to early Indosinian time.The type A2 crude oil is of wide distribution in this area. Its generation, migration, accumulation and pool formation time was later,chiefly in the Mesozoic and even still later time. Most oil pools found in the Permian sediments in this area belong to this type.