Abstract: Applying the method of single factor analysis on the basis of comprehensive evaluation with structure,sandstone,and the model of hydrocarbon accumulation,the mechanism of ternary factors coupling for controlling reservoir has been understood,and beneficial exploration areas for Paleogene stratigraphic reservoir of Qikou Sag in Huanghua Depression of the Bohai Bay Basin were revealed.It indicated that the major controlling factors of forming reservoir could fall into three categories: first was oil source including hydrocarbon-generating,expulsion and transportation system;the second was physical property of reservoir including properties of porosity,permeability and characteristics of pore structure;the third was whether the trap was effective or not(storage oil or not)and the closing height of trap(deciding the output proportion of oil and water).The major factor of deciding distribution of traps were whether paleo structural setting was matched with depositional systerms.New patterns of "Ternary Factors Coupling" controlling reservoir-forming can be used to express the essence of pool-forming.There are large scale beneficial exploration areas for Paleogene stratigraphic reservoir in Qikou Sag such as Banqiao-Binhai faulted-nose,Binhai slope area and Chengbei fault ramp.