Natural gas flow was obtained during the production test in the Upper Triassic in Luoyi Sag. In order to clarify the development characteristics of the large boundary fault，hydrocarbon generation，reservoir formation and hydrocarbon accumulation，based on the analysis of a large number of drilling，boreholes，key outcrops and new and old 2D seismic data，the development characteristics，evolutionary stages and the controlling effect on hydrocarbon accumulation of the southwest boundary fault in Luoyi Sag are studied in detail according to the seismic and geological data，fault patterns and basin dynamics. The results indicate that ① Fault YY is a complex regional deep fault，which can be divided into four sections：imbricated strong overthrusting section，negative inversion section after trust and extrusion，multi-angle imbricated strong overthrust superimposed strike-slip structural section，and asymmetric ox-imbricated strong overthrust section. ②Luoyi Sag has experienced five stages of structural evolution：weak extensional rifting in the middle and late Hercynian period，weak compression and uplift deformation in the early Indosinian period，unbalanced depression in the late Indosinian period，strong overthrust uplift and denudation in the Yanshanian period，and sinistral strike slip rifting in the Himalayan period. ③The tectonic activities of Fault YY not only controls the development characteristics of hydrocarbon source rock in Permian，Triassic and lower-middle Jurassic，and multiple secondary hydrocarbon stages in late Indosinian and Yanshan-Himalayan period，but also controls the development series of strata and zones of favorable reservoirs such as underwater distributary channel sandstone along the tectonic transformation belt，as well as the fracture transformation of tight sandstone reservoirs. Meantime，the fractures also has a destructive effect on the hydrocarbon accumulation of Permian and Mesozoic periods in the study area. ④The three zones in the north of Yima sub-sag are more favorable for hydrocarbon accumulation in Permian and Mesozoic periods.