Abstract: Abstract：Based on a comprehensive analysis of the generation characteristics of source rocks as well as the difference and the quantitative evaluation of fault activity, the authors studied the relationship between the difference of fault activity and the Neogene hydrocarbon enrichment during the hydrocarbon generation period in Qikou Sag of Bohai Bay Basin. The results show that the fault activity differences during the main hydrocarbon generating periods from Neogene to the present can be divided into five categories, i.e., the early-acted-late-declined type, the gradually-acted-turned declined type, the gradually-declined-turned acted type, the early declined-late acted type and the acted stable type. The relationship between the difference of fault activity and the Neogene hydrocarbon enrichment can be revealed by the fault activity difference coefficient (FDC). According to the fault activity rate in the phase of the Minghuazhen Formation and the fault activity difference coefficient,the faults are divided into 3 types, namely Ⅰ, Ⅱ and Ⅲ. Hydrocarbon is mainly concentrated in the favorable traps controlled by type Ⅰand type Ⅱ faults whose activity rate and FDC are relatively high. The enrichment of oil and gas is poor in the traps controlled by type Ⅲ faults whose activity rate and FDC are relatively low. The scale of oil and gas migration is controlled by fault activity rate, while the extent of hydrocarbon enrichment is controlled by FDC.