Grey literature is produced and widely applied in the researches of science and technology, as an important reference source. Developed countries pay great deal of attentions to the collection of the important grey literature. Different departments of Chinese Association for Science and Technology (CAST) have accumulated a great many of academic conference proceedings and working documents, majority of which belong to the category of grey literature. In order to manage better the grey literature produced by Chinese Association for Science and Technology, a grey literature classification system is proposed based on the organizational structure of CAST, which is divided into four levels. The first and second level categories are constructed according to the organizational structure of CAST, with the first category reflecting the three basic sources of CAST literature, that is, from Chinese Association for Science and Technology, from national societies and from local associations of science and technology, and with the second category reflecting subordinate institutions under the first level. The categories of the third and forth levels are constructed according to the publication types and the publication years of literature, respectively. This classification system may better reflect the achievements made by different departments of the CAST, and facilitate the handling of the literature.