After reflection on some common assumption in English teaching and learning,the article probes such terms as vocabulary size and lexical knowledge,the common practice and weaknesses in college English teaching and learning.

<Abstrcat>This paper explores three phases of understanding lexical knowledge from a cognitive point of view in vocabulary learning.

The author holds that too much emphasis has been put on the vocabulary enlargement, while the deepening of lexical knowledge is comparatively neglected.

However,owing to an insufficient understanding of vocabulary knowledge,college English learners have failed to devote enough attention to the study of high frequency words.

This study examines the role of vocabulary knowledge in oral communication,focusing on three essential aspects of word knowledge components: pronunciation,lexical meaning and collocation.

Based on the theory of Vocabulary Pragmatics and other research, this paper first analyzes vocabulary knowledge, including the form, the pronunciation, the meaning, the collocation, the function, and the association of words.

Related research on the use of vocabulary strategies and level of word knowledge;

And it looks into the relationship between vocabulary size and word knowledge types(i.

With the analyzing the subjects oral production, the results manifested three diversity: (1) the results of sub-indices of word richness consistently increased, while the result of sub-index of word knowledge(phonological errors) took on an increasing tendency.

In this paper, one aspect of vocabulary, that is word association knowledge has been proved to facilitate vocabulary retention, to enlarge one’s vocabulary size.