Abstract Background Pneumonic-type invasive mucinous adenocarcinoma (IMA) was often misdiagnosed as pneumonia in clinic. However, the treatment of these two diseases is different. Methods A total of 341 patients with pneumonic-type IMA (n = 134) and infectious pneumonia (n = 207) were retrospectively enrolled from January 2017 to January 2022 at six centers. Detailed clinical and CT imaging characteristics of two groups were analyzed and the characteristics between the two groups were compared by χ2 test and Student’s t test. The multivariate logistic regression analysis was performed to identify independent predictors. Receiver operating characteristic curve analysis was used to determine the diagnostic performance of different variables. Results A significant difference was found in age, fever, no symptoms, elevation of white blood cell count and C-reactive protein level, family history of cancer, air bronchogram, interlobular fissure bulging, satellite lesions, and CT attenuation value (all p < 0.05). Age (odds ratio [OR], 1.034; 95% confidence interval [CI] 1.008–1.061, p = 0.010), elevation of C-reactive protein level (OR, 0.439; 95% CI 0.217–0.890, p = 0.022), fever (OR, 0.104; 95% CI 0.048–0.229, p < 0.001), family history of cancer (OR, 5.123; 95% CI 1.981–13.245, p = 0.001), air space (OR, 6.587; 95% CI 3.319–13.073, p < 0.001), and CT attenuation value (OR, 0.840; 95% CI 0.796–0.886, p < 0.001) were the independent predictors of pneumonic-type IMA, with an area under the curve of 0.893 (95% CI 0.856–0.924, p < 0.001). Conclusion Detailed evaluation of clinical and CT imaging characteristics is useful for differentiating pneumonic-type IMA and infectious pneumonia.