Abstract: Through the detailed analysis of seismic, drilling and well logging data, the Cenozoic of Maichen sag in Junggar basin can be divided into three structural zones from the bottom up: Changliu formation?Liushagang formation, Weizhou formation and Neogene?Quaternary. They correspond to such three structural evolution stages as continental rift stage, rift?depression transition stage and marine depression stage. The transition changes of the three stages result in two transformations of structural pattern of this sag: at the end of Eocene the Junggar basin’s pattern transformed from NE to near EW; at the end of paleogene the whole basin was uplifted and eroded, becoming regional depression from rift. At the same time, the differences of structural evolution made the different structural styles developed in different structural zones: the stress in the lower structural zone (Changliu formation-Liushagang formation) was dominated by tension, developing stretch structural style; the stress in the middle structural zone (Weizhou formation) was tension and strike?slip, mainly developing stretch and strike?slip style, and in the upper structural zone (Neogene-Quaternary) few or no fault occurred