This paper develops"the boundary change theory"of le in modern Chinese on the basis of the overview and summary of previous research and draws the conclusion that the boundary change of le can be defined as a functional semantic expression.The boundary change is considered to be related to semantic categories in the broad sense such as action/property,situation type,modality,voice,tense,topic,and can show the change of state from those different semantic hierarchy and semantic scope.Furthermore,the paper points out the limit of tense-aspect theory in morphological grammar and responds to the doubt of one le theory.We believe that only by changing the research paradigm and establishing a theoretical structure of cognitive typology can we establish a theory of le which possesses a general grammatical significance and be able to disengage from the impact of tense-aspect theory in morphological grammar.Based on the concept of linguistic cognitive typology,this paper argues that the boundary change is also a semantic type easily perceived in linguistic cognition,and thus easily grammaticalized as a syntactic category.Therefore,by taking the boundary change as the axis,a comprehensive examination to the relationship between the front and back boundary change interfaces and their impacts may be an effective way for grasping the syntactic representations of Chinese situation types.Accordingly,based on the boundary change theory,we classify the boundary change types as follows:boundary change type {Azeroboundary change B.state-boundary change(b1/b2/b3)C.qualitative-boundary changeThis classification,which takes the boundary change as the axis and compares the state of the interface before and after the boundary change at the same time,takes the combination of the interface and the boundary change as the object of observation.The classification,thus based on the combination of the interface and the boundary change,not only explains the co-occurrence of various types of boundary change with le in a simple and clear way,but also covers the types of boundary change by the semantic combinations of action and result complements,and tendency complements,which is simpler,more general,and more explanatory.Meanwhile,in order to prove the validity of the point of view above,this paper searches for the sentences with le in Mao Dun's short story Lin Jia Pu Zi(The Shop of the Lin Family),and obtains a total of 443 cases,and summarizes 11 kinds of sentences with le.We examine each of these sentence patterns through the lens of the boundary change theory,thereby substantiating the validity of this theory.