The Dagang oil field is located in the huanghua basin of the north China.It has been undergone five stages of tectonic thermal events.They are Caledonian,Hereyhian,Indo-China,Yanshanian and Himalayan.The result of researching paleo-fluid shows that two stages of paleo-fluid migration are taken place in this area.They are separately in yanshanian and Himalayayan,and is called as early stage and late stage.The features of fluid inclusion,composition and physio-chemical properties are very different between early stage and late stage.The liquid hydrocarbon inclusion is dominent in fluid inclusions of early stage,and the gas-liquid hydrocarbon inclusion is major in fluid inclusions of late stage.The content of organic composition is smaller(13.5-37.9wt%)than inorganic composition(62.0-85.9wt%) in fluid inclusion of early stage.The content of organic composition is higher(34.6-73.0wt%) than inorganic composition(26.6-65.2wt%) in fluid inclusion of late stage.Temperature and pressure is very different in fluid inclusions of early and late stages.The temperature is smaller in early stage(100-120 C) than in late stage(135-150 C).The pressure is higher in late stage(17-46Mpa) than in early stage(16-43Mpa).The pH value and Eh value of paleo-fluid is slightly smaller in early stage than in late stage.The above data indicate that two stage of oil-gas migration is existed in this area.