Abstract：The Shulu subbasin lying in the southwestern part of the Jizhong depression is a typical single-downfaulted subbasin in an extensional system. Its structure is simple with a NE extensional fault system and a NW-trending transverse accommodation zone. Based on the evolutionary history and drilling well data of the subbasin, this paper discusses the mechanism and time of formation of this transverse accommodation zone and proposes that the first-order accommodation zone formed in a stage of strong extension of the subbasin, while the second-order accommodation zone formed in a stage of weak extension of the subbasin. The formation of the first-order transverse accommodation zone is controlled by inhomogeneous extension of the boundary fault and basement uplift, the deference in lithologic association is the trigger mechanism of the second-order transverse accommodation zone, and the alternating development of en-echelon faults that control the subbasin is the dynamic mechanism of formation of the second-order transverse accommodation zone.