Avoidant personality disorder (AVPD) can result in impairment of the individuals' daily functions, including mental health, social and physical aspects. AVPD is not only one of the most serious personality disorders, but also one of the most popular personality disorders. This paper reviews the personality characteristics and symptoms, causes, measurement, and treatment of AVPD, further expounds the differential diagnosis of AVPD from other psychological disorders from the perspective of psychodynamic theory, and shows that biological factors such as heredity and temperament, early childhood experience, attachment style, and family environment are all possible causes of AVPD. Some measurement tools and treatment methods for AVPD have been developed, but there are still limitations. More research is needed to develop more measurement and treatment methods specifically for AVPD in the future.