Abstract: On the basis of studying fault system, for example, Dongying Formation of Dongxin Oil Field in Dongying Depression, the closing of faults was studied and the relation between normal stress of fault plane and closed ability was found.The arcuate faults have the special closed capability for petroleum accumulation, the stress mechanism and form process of arcuate faults in complex block oil field were discussed.The characteristic of arcuate fault section and closed mechanism were studied too.The closing of arcuate fault in complex block oil field is better than others, which is important to searching for the secondary oil pool forming in the stress combine and structural edge.