This study focuses on the space of English vowels and how each pair of tense-lax vowels can be identified according to the accurate phonetic features.The positions or heights of the tongue have been believed to be elements that determine how to pronounce a vowel.However,data in this study show that there is another feature that can tell the difference between the tense-lax vowels-the tense vowel and lax vowel in the same phonetic space move in various directions,mostly opposite to each other.This finding may help EFL learners in two aspects:recognition of these characteristics may benefit EFL learners in Nanchang Institute of Technology so that they can sense the subtle differences of the tense-lax vowel pairs and acquire confidence in English pronunciation.