Abstract: Viewed from the perspective of the doctrines of "dirty hands" and the reason o f state, it follows from the appeal to the legitimacy of ends in public administ ration that illegitimate means have to be adopted. The distortion of ends themse lves will be unavoidable under the single-minded pursuit of legitimacy of ends, so that the dual legitimacy of ends and means will be out of reach in public ad ministration. Meanwhile, it may also lead to an ethical dilemma in which the pub lic administrators and those administrated scramble for the same moral highland. Modern public administration must seek for the dual legitimacy of ends and mean s. The theoretical foundation for this is the constitutional reason of state, an d the practical choice is the administration by law.