Objective To explore the mechanism of personality between attachment and defense style in college students. Methods 291 students were surveyed with Eysenck Personality Questionnaire-R Short Scale (EPQ-RSC, Chinese Adaptation), Experience of Close Relationship Inventory(ECR, Chinese Adaptation) and Defense Style Questionnaire ( DSQ). Results ①Unmature defense style had significant positive correlations with anxiety, avoidance, neurotism and psychoticism(r = 0. 19,0.45,0.51,0. 19, P<0.01) ,and had significant negative correlation with extroversion(r= -0. 25, P<0. 01 ) . ②Extroversion acled as part meditator between attachment and unmature defense style. ③Neurotism served as part meditator between anxiety and unmature defense style. Conclusion Attachment is a remarkable predictor of unmature defense style and has indirect influence on it through neurotism and psychoticism.