Objective To explore the clinical application value of CT in the diagnosis of diffuse chest diseases. Methods 115 patients diagnosed with diffuse chest diseases who were admitted in the hospital between June 2011 and July 2014 were selected as the study subjects. All patients underwent chest CT and X-ray examination. The image quality and positive rate were compared between the two kinds of examination methods. The chest CT findings of patients with different diseases were recorded. Results The excellent rate of X-ray film quality (68.7%) was significantly lower than that of chest CT images (87.0%) (P<0.05). CT examination results of 115 cases of subjects were all positive and the positive rate was 100.0%. A total of 25 cases of chest CT images were with scattered patchy shadows (including 9 cases with interstitial pneumonia, 1 case with hylactic pneumonitis, 7 cases with pulmonary sarcoidosis, 2 cases with radiation pneumonitis, 6 cases with idiopathic pulmonary fibrosis). Lesions showed ground glass shadow in 35 cases, nodule shadow in 33 cases, honeycombing shadow in 4 cases, reticular shadow in 13 cases and miliary shadow in 5 cases. X-ray examination results showed that 93 cases were positive and the positive rate was 80.9% (P<0.05). Conclusion Compared with chest X-ray film, chest CT images are more distinct, which is more favorable for doctors to observe the image features, and accurately determine the type of disease.