According to the theory of fuzzy set by J. Zaden, the American Scientist, children's literature can be regarded as a fuzzy set. First, "children" and "literature" , as the fundamental properties of children's literature, are both fuzzy words with fuzzy semantics which makes the term "children's literature" an assembly made up by fuzzy concepts. Next, the denotation of the term "children's literature" is also fuzzy. The range of writers, texts and readers are all fuzzy. These three fuzzy factors form another fuzzy set. There are several reasons that make the concept of children's literature a fuzzy set. One of them is from the object with which this term deals--the complexity of the creation of children's literature, which is the result of children's intuition. "Everything in intuition is primeval, sheer, obscure, individual and integral." The only thing that can express a writer's intuitive feeling is image. Peculiarity is always needed for a creation of the literature. However, if one wants to get a definition of children's literature, one needs to express it in rational and logical language, which is obviously ridiculous. The minor details removed, only dullness is left, which is impossible to express precisely the object with which it deals. Children's literature is always a developing process. It is colorful, excessive and profound. Every theory, limited by the history, can only define it from a certain point of view. It is impossible to define the ever changing children's literature from a fixed point. All above are the reasons that explain why the concept of children's literature is a fuzzy set.