Abstract: DaLiuquan structure zone of Langgu Depression is a large nose structure zone.The Jiuzhou fault , in the middle of DaLiuquan structure zone , plays an important role in the migration and accumulation of oil and gas.The indicator of synthetic evaluation of Jiuzhou fault sealing property includes fault activity , lithologic association on two sides of fault , mudstone smearing , rate of mud in fault stuff and the stress of fracture surface analysis.The results show that Jiuzhou fault starts and grows intensely in the third Shahejie and Dongying sedimentary period.It fits to the hydrocarbon migration periods in this area.So the fault could become the pathway of hydrocarbon migration for oil and gas reservoir of the middle third Shahejie formation.The feature of Jiuzhou fault sealing is'lower good and upper bad'on the whole , and northern region is better than the southern , which due to the difference of north and south reservoir.