Abstract: The Ne bis in idem's connotation and mechanism of action need to be defined.We can clarify the connotation of Ne bis in idem by comparing it with res judicata and repeated litigation.The ne bis in idem under the dual norm's mechanism of action is as follows;As a norm for conduct,it can identify " the same case" via litigant,declaration of litigation and main issues synthetically,thus to deny the repeated sue.As a norm for evaluation,it can evaluate different types of "the same case" under "Er Tong",thus to counterclaim,consolidate,stay of action inflexibly.