This study selected ninety - nine outpatients and inpatients with obsessive - compulsive disorder (OCD)in Nanjing Brain Hospital for two longitudinal follow-up surveys with an interval of 3 months to explore the relationship between absolute belief，catastrophizing beliefs and obsessive - compulsive symptoms and their interactions. We adopted the Yale - Brown Obsessive - Compulsive Scale(Y - BOCS)to measure the severity of obsessive -compulsive symptoms; the Absolute Belief Scale and Catastrophic Belief Scale to assess the level of beliefs; and the Obsessive - Compulsive Belief Questionnaire(OBQ)to measure obsessive - compulsive beliefs. Bootstrap results revealed that catastrophizing beliefs fully mediated between absolutizing beliefs and obsessive- compulsive symptoms in patients diagnosed with OCD，with a mediating effect size of 0.02(95% CI: 0.01~ 0.03). The cross - lagged regression showed that the absolute beliefs related to others in the pretest had a significant predictive effect on both self-evaluation(β=0.238，P＜0.05)and others’evaluation(β=0.278，P＜0.05) of catastrophizing beliefs in the posttest. In conclusion，catastrophizing beliefs of OCD patients may fully mediate between absolutizing beliefs and obsessive - compulsive symptoms. The others related factor in absolutizing beliefs predicts the belief levels of both self- and others-rated factors in catastrophizing beliefs.