Guided by the three - dimension grammatical theory and cognitive gra mmar theory and based on the categorization of Complements in Modern Chines e, this paper , integrating the theory research with concrete problems analysis, explores the most salient features of complements and seeks the relevance between various complements so as to have a clearer and more comprehensive grasp of the system and functions of Chinese complements. This paper concludes that the structure feature and functions of complements are closely related with the .time. and .quantity. categories. The paper includes six chapters; they are Introduction, four chapters of the main body, and Conclusion. The part of Introduction is mainly concerned with the significance of complements research, the theoretical framework the paper adopts and the research scope. We also give a brief account of the data source and the symbols we will use in the paper. A brief retrospection of the research of Modern Chinese complements previously done as well as comments has been given in Chapter two . We classify the previous study in to four periods, with the intent of combing comprehensively the characteristics and achievements of the study on complements in different periods and pointing out their weakness. Chapter three deals with the characteristics and classification of complemen ts. Concentrating on the linear order of predicative and complement, we believe that the complement structure falls short of congruence, but it functionally plays a role in the delimitation of predicative. Based on the .time. category, we classify compleme nts into temporal process complement and temporal quantity complement. Based on the prototypicality effect, we classify complements into prototypical complement and non - prototypical complement. In this chapter, we have discussed the delimitation of noun p hrase, quantity phrase and prepositional phrase from the perspective of cognitive prototype theory and valency theory. 7 Chapter four is mainly about the analysis of the quantity that complement possesses in the complete predicative - complement structure. According to the semantic meaning that complements express, we divide prototypical complement into quantity complement and non - quantity complement. While non - prototypical complement is divided into variant complement, contrastive complement and modal compl ement. In this chapter we have also discussed the grammaticalization of some complements, pointing out the two directions in which the complement grammaticalization will develop. On the one hand, the delimitative role complements play will enhance the deve lopment in the direction of .aspect markedness.; on the other hand, the closeness the predicative and complement possess will enhance the development in the direction of .lexicalization..