Objective To analyze the value of CT scan in the diagnosis of patients with pulmonary diseases. Methods The clinical data of 74 patients with pulmonary diseases in our hospital were retrospectively analyzed. All patients underwent CT scan and biopsy after admission. The coincidence rate of CT diagnosis and pathological examination was compared. The CT findings and diagnostic value in pulmonary diseases were analyzed. Results CT detected 24 cases with benign lung lesions, including 11 cases (91.67%) of fibrous tissue hyperplasia, 7 cases (100.00%) of pneumonia, 5 cases (100.00%) of pulmonary tuberculosis, 2 cases (50.00%) of atypical adenomatous hyperplasia. There was 1 case of hamartoma misdiagnosed, 1 case of fibrous tissue hyperplasia and atypical adenomatous hyperplasia missed diagnosed; CT detected 42 cases with lung malignant lesions, including squamous cell carcinomas in 20 cases (90.91%), adenocarcinomas in 15 cases (93.75%) and undifferentiated carcinomas in 7 cases (87.50%). The overall consistency with pathological examination was 89.19%. Conclusion In the diagnosis of pulmonary diseases, the application of multi-slice spiral CT scan is of high resolution to soft tissues, noninvasive, with good reproducibility which has higher detection rate of benign and malignant lung lesions and the high consistency with pathological examination. It is of high clinical application value