Objective To investigate the application value of multi-slice spiral CT in the diagnosis of chronic obstructive pulmonary disease (COPD). Methods A total of 120 cases of patients with chronic obstructive pulmonary disease who were admitted in the hospital from January 2018 to December 2019 were selected as the subjects. All the patients were divided into the mild group (n=36), the moderate group (n=30), the moderate-severe group (n=24), the severe group (n=18) and the extremely severe group (n=12) according to results of forced expiratory volume in one second prediction (FEV1%). The five groups were diagnosed by multi-slice spiral CT. The detection rate of multi-slice spiral CT for different degrees of disease and the cross-sectional area of pulmonary small vessels in the five groups were compared. Results A total of 22 patients with mild chronic obstructive pulmonary disease were detected by multi-slice spiral CT, with the detection rate of 61.11% (22/36). A total of 21 patients with moderate chronic obstructive pulmonary disease were detected, with the detection rate of 70.00% (21/30). A total of 17 patients with moderate-severe chronic obstructive pulmonary disease were detected, with the detection rate of 70.83% (17/24). A total of 14 patients with severe chronic obstructive pulmonary disease were detected, with the detection rate of 77.78% (14/18). A total of 11 patients with extremely severe chronic obstructive pulmonary disease were detected, with the detection rate of 91.67%(11/12). The blood vessel/lung cross-sectional area of sub-segment level and below (%CSA<5) and blood vessel/lung cross-sectional area of CSA sub-segment level (%CSA 5-10) in the extremely severe group were lower than those in the severe group, the differences were statistically significant (P<0.05). The blood vessel/lung cross-sectional area of sub-segment level and below (%CSA<5) and blood vessel/lung cross-sectional area of CSA sub-segment level (%CSA 5-10) in the severe group were lower than those in the moderate-severe group, the differences were statistically significant (P<0.05). The blood vessel/lung cross-sectional area of sub-segment level and below (%CSA<5)and blood vessel/lung cross-sectional area of CSA sub-segment level (%CSA 5-10) in the moderate-severe group were lower than those in the moderate group, the differences were statistically significant (P<0.05). The blood vessel/lung cross-sectional area of sub-segment level and below (%CSA<5) and blood vessel/lung cross-sectional area of CSA sub-segment level (%CSA 5-10) in the moderate group were lower than those in the mild group, the differences were statistically significant (P<0.05). Conclusion Multi-slice spiral CT in the diagnosis of chronic obstructive pulmonary disease has better effects, it can objectively evaluate the severity of the condition. The more severe the condition of patients, the smaller the area of pulmonary small vessels.