| The United Nations is a community barometer on the changing international society. As to the only universal international organization;The United Nations devoted to seek world peace and security. The United Nations and International Security have closely connection. UN collective security mechanism applied to collective security’s thinking in the United Nations creatively, by the hands of the United Nations, to achieve collective security purposes. However, collective security is the idea about an idealized thought on the nature of in the international community.In the state of anarchy, every country follows the instinct of self-security awareness. Additionally, in recent years, the international community is not peaceful, traditional and non-traditional threats affecting the peace and security of the international community interwoven. The United Nations collective security mechanism is challenged by a lot of external force frequently. Such as, the challenge of terrorists, the instead of national administration;the challenge of narrow nationalism; the challenge of tight budget, the insufficiency of cultural identity; These external challenges and difficulities lead to the onward march of the united nations. To make matters worse, whether in the decision-making mechanism of the United Nations level, or in terms of dimensions and mechanisms, or in terms of nuclear disarmament arms control, regional coordination level, more or less on the performance of weakness and compromise. The people will be more suspicious of the Mechanism of UN on authority and efficiency. In this paper, through the use of chart analysis method, the literature analysis method, theory and history combined with other methods of defects for the UN collective security mechanism to specifically addressed, and noted that the cause of these defects. The purpose of the UN collective security mechanism is be for peace and human security services, which is the root of the mechanism with vitality. To make the mechanism of action of the play better, reform of the UN collective security mechanism is imperative. |