Abstract: The primary factors which affect learners' foreign/second language attrition are their language acquisition, linguistic level before attrition and exposition to foreign language during attrition, time duration of language attrition, age and social affective causes. The study of these factors of language attrition will help us determine the most appropriate time for ESP vocabulary teaching, take effective strategies for ESP vocabulary training, guide students to cultivate correct attitude towards study and improve their ESP learning after their graduation