The formation mechanism and hydrocarbon accumulation control of the transtensional structure in the study area are studied comprehensively with geologic and geophysical and numerical simulation methods with qualitative analysis and quantitative evaluation to improve the understanding of the development and evolution mechanism of the transtensional structure and its effect on the controlling factors of hydrocarbon accumulation in Linnan area. Results demonstrate that the Linnan area first stretches obliquely due to extensional force，and then a typical transtensional structure is formed because the reactivated basement fault strike is oblique to the extension direction of the area. Considering horizontal extension，vertical block faulting and lateral strike-slip movement，a quantitative characterization method of the transtensional structure are established. The average intensity of transtensional activity is about 0.4. The reservoir development is obviously controlled by the extensional structure. Three sand control modes of gentle slopes with stable subsidence，continuous migration and subsidence and slopes with synsedimentary faults affect the formation of different traps. The accumulation modes of dynamic equilibrium in the transtensional fault zone，lateral migration in the slope zone and self-generation and self-storage in the sag zone are established according to the four structures of fault zones，namely ternary，binary，unitary and unstructured modes.