Abstract: Objective To obtain the three-dimensional shape of the diaphragm in patients with COPD by three-dimensional reconstruction with 64-slice spiral CT, and to explore the relationship between the morphological indexes of diaphragm and the COPD Assessment Test(CAT). Methods The subjects of outpatient and inpatient in Ningbo No.2 Hospital from December 2010 to October 2014 were divided into the COPD group(30 patients) and the control group(20 patients) according to the 2007 criteria of Chinese Respiratory Society for the diagnosis and treatment guidelines of COPD. All the subjects were taken pulmonary function test, CAT and lung CT scan. The main morphological indexes of the diaphragm after CT three-dimensional reconstruction including the total diaphragm length(Ldi), the total diaphragmatic area(Adi), and the surface areas of the zone of apposition(Aap) were obtained and compared between patients with different severity in the COPD group. The correlation between these morphological indexes and CAT scores were analyzed. Results ① With the increase of the severity of COPD, the coronary Ldi and sagittal Ldi, the total diaphragmatic area and surface areas of the zone of apposition decreased gradually, and the CAT scores increased gradually, and there was significant difference among different COPD severity groups(all P<0.05). ② The total diaphragm length, the total diaphragmatic area, and Aap were negatively correlated with the CAT scores of COPD(all P<0.05). Conclusion CT three-dimensional reconstruction is a reliable method for evaluating the functional anatomy of the diaphragm, which can be used to evaluate the function of the diaphragm in COPD patients.