Objective To analyze the findings and characteristics of multi-slice spiral CT before and after lavage therapy of pneumoconiosis. Methods The clinical data of 50 patients with pneumoconiosis in Clinic were analyzed retrospectively. All patients were treated by large-capacity alveolar lavage and underwent multi-slice spiral CT examination and the imaging data were complete. The improvement of lung volume and lung density indexes in the patients before and after the treatment was statistically analyzed. Results After large-capacity alveolar lavage, total lung volume and total lung containing gas volume of the patients increased slightly but there was no statistical significance, compared with those before lavage (P>0.05). After lavage, the total lung weight was reduced, average lung density decreased and average lung volume increased. Compared with those before lavage, the differences were statistically significant (P<0.05). The changes of total lung weight were the most significant, followed by lung CT value, average lung density and lung volume. Conclusion After large-capacity alveolar lavage, the changes of multiple spiral CT quantitative and qualitative indexes such as lung density and lung volume and changes of pulmonary function indexes in patients with pneumoconiosis were well correlated, which can be used as the basis for the evaluation of the curative effect in patients.