Objective To explore the application value of multi-slice spiral CT (MSCT) plain scan before and after clinical treatment of active tuberculosis. Methods 118 patients with active tuberculosis collected from our hospital from December 2016 to August 2018 were selected as subjects. All patients were treated with antituberculosis therapy. MSCT was performed before and after treatment. The clinical and imaging data of 118 patients with active tuberculosis were analyzed and compared. The results of MSCT images before and after treatment were compared. Results The detection rate of active pulmonary signs in 106 patients with active tuberculosis before treatment was 100.00% (118/118), and the detection rate of active pulmonary signs in MSCT after antituberculosis therapy was 38.98% (46/118),and the difference was statistically significant (χ2 =121.026, P<0.001). According to the relevant imaging data, after antituberculosis therapyt, the MSCT examination showed that in the CT signs of the patients with active tuberculosis,the absorption rate of shadow like frosted glass, tree-in-bud, bronchial thickening and segmental distribution of leaflet central nodes can reach more than 80.00%, and plaque and spherical lesions were partially absorbed,which indicated the uncertainty of the activity of tuberculosis. However, there was no significant change in the signs of bronchiectasis and fibrous stripes and hachure in MSCT examination before and after treatment, which suggested that this sign was the main sign of residual tuberculosis after antituberculosis therapy. Conclusion MSCT can clearly show the signs of active tuberculosis and it is useful to observe the evolution and transformation of signs lung before and after treatment. It is more helpful to evaluate the therapeutic effect of patients with active tuberculosis and provide further guidance for their treatment.