Public interest factors difficult to define the definition of public interest has always been a difficult, all these comments never uniform, so that the prestigious American Library Lang Chief ethicists believe that the public interest and non-political myth of the existence of this unclear what is always said, to give a theoretical circles or get recognized by practitioners of "public interest" definition is almost impossible. Well-defined public interest, the real reason may be related to the following factors: first, social life, people have seen is the public interest to pay and enjoy the existence of asymmetry is often the case. Different public interests and private interests, private interests are directly on individuals and their relatives and close friends, all good things, it enables individuals directly feel the value and significance of its existence; and the public interest, as a whole exists, it Identification is not easy to grasp. Public interest in the pursuit of the process is very easy to pay and enjoy the asymmetry exists, not only in acts inconsistent on the subject (such as those who pay are not just trying to enjoy), but also in the object's inconsistent on (such as national, Government investment in education, and citizen access to the improved social order), plus as an individual, the reality of limited human knowledge, but also increased the difficulty of identify the public interest. People tend to care about the interests of known or obvious, but when it comes to the possibility of many people and the unpredictable future, they will become hesitant, and even short-sighted up, the public interest because such reasons are often to be sacrificed. Second, the practice of public administration, people positioning themselves for the public interest also is fuzzy. Everyone knows that the public interest within a certain social group is to maximize the benefits. Bodenheimer United States on the concept that the public interest "means that the distribution and exercise of individual rights must not go beyond the outer limit." But in the real social life, how great this piece of interest to become a real public interest is difficult to define. As the public interest no borders, it is difficult to measure, in practice, and will have a mere figurehead or the possibility of distortion. If a government department to place the interests of the department of public interests, or units to the leadership of his own will above the control department of the public interest, public interest in the real world tend to be replaced on into "departmental interests", "local interests" and "organizational interests." It should be said, as opposed to personal interest, which undoubtedly has a certain degree of public resistance, but they are not necessarily bound to be a real public interest. It is actually just a certain level of "community" interests. Pursuit of public interest as a value is a whole community can not be divided one by one with the nature of departmental interests. Although each functional department of public administration is to achieve the public interest to be part of, however, after the formation of each department once, it will rise to their "community interest", they are often in their own community's interests under the banner name of public interest confrontation with the real public interest. Thus, people of public interest and the interests of the public body is dissolved the distinction between the boundaries. Third, the public interest, the manifestation of diversity. The largest community of human society is in fact a number of community-level sub-component according to certain rules, the high level of community interest restricting low-level community interest may exist between some forms of conflict. For example, we can as human society by the nations of the world community, the State itself can be regarded as a sub in the community, government departments and local governments can be seen as Zaici a Community, and more. We usually call "departmental interests" and the "local interest" here can be understood as lower-level Community interest, such as citizen housing, medical care, education and transport. In this way, in fact as a public entity, each individual's personal interests are real, clear, but that specifically targeted the public interest is invisible, both showed the concentration of individual interests, personal interests are not full stack, it can not be simply interpreted as each individual based on personal interests arising from common interests, and therefore it appears difficult for its positioning. Because it is difficult to all the population in a particular period or a particular area of interest is what the public consensus, can only obtain the minimum divisor, to at least one step closer to the public interest.