Although Selective Serotonin Reuptake Inhibitors(SSRIs) and Cognitive Behavior Therapy (CBT) including Exposure and Response Prevention(ERP) are two kinds of the first line treatments for OCD(Obsessive-Compulsive Disorder) according to APA（American Psychological Association）guideline. Both of the treatments are effective, but few research has been done to find out who are more responsive to one treatment than the other. The aim of our research is to evaluate the efficiency of SSRIs ,ERP and the combination of the two therapies for OCD patients ,at the same time, to find out the biological and psychological predictors of treatment response in Chinese population.