| "Neng", "Hui" and "Keyi" is a comparatively hard nut in teaching Chinese as a foreign language. There are many studied on the three words in the literature, but the problem still exists in teaching. In this paper, in order to solve the problem, we carry out a comprehensive inspection and analysis about the basic meaning of"Neng","Hui"and"Keyi"in the content domain, epistemic domain and speech act domain under the guidance of Cognitive Linguistics theory. We compared the different path of each from the core meaning to the non-core meaning development, the quantity of subjectivity and the pragmatic functions and analysed their similarities and differences. Based on this, we analysed the main error of the modal verb and put forward constructive views for Teaching Chinese as a foreign language. |