Based on systematic analysis of fault systems and its evolution in the Beier Sag, Hailaer Basin, the control of fault formation and evolution on hydrocarbon migration and accumulation was researched. It is concluded that there were four types faults which were early extensional faults, middle tensional—shear faults, early extensional middle tensional—shear longterm active faults and early extensional middle tensional—shear late inverse longterm active faults, and three fault systems which were early extensional fault systems, middle tensional—shear fault systems and late inverse fault systems. There were three fault active periods in the Beier Sag. The first, from depositional time of the Tongbomiao Formation to end that of the Nantun Formation,formed early extensional fault systems with extensional deformation under NW—SE tension stress fields . The second, when the 2nd and 3rd Member of the Yimin Formation deposited,formed middle tensional—shear fault systems with pure shear deformation under closely EW tension stress fields. Final, from end depositional time of the Yimin Formation to that of the Qingyuangang Formation,formed late inverse fault systems with contraction deformation under closely EW extrusion stress fields.Fault formation and evolution controlled formed period, growing types and distributed directions of traps. Longterm active faults were major transporting hydrocarbon fault types in the Beier Sag. Around sourcerock, the basement block traps, tilted block and normal drag block traps with controlled by source faults were favorable areas of hydrocarbon migration and accumulation.