Under the structuralism of traditional grammar, former scholars have explained the College of Literature, Sichuan Normal University. Chengdu, Sichuan 610068words “Shangqu” (上去）and “Xiaqu”（下去）from the directions of act and the semantic grammaticalization in detail when they are used as directional complement. For example, “Reng Shangqu”（扔上去）and “Diu Xiaqu”（丢下去）are content words and express the direction of act; “Xiao Xiaqu”(笑下去）and “Kan Shangqu”(看上去）are semantic weakening. Comhining these former views, we will discuss the conditions of existence and collocations of these two words as complement in the cognitive way, especially using the Image Schema Theory as well as the Prototype Theory and the view of metaphor, to reveal the mechanism and imbalance of grammaticalization.