Objective To explore the clinical effect of antibiotic step-down therapy in patients with severe diabetes pneumonia. Methods? A total of 80 patients with severe diabetic pneumonia admitted to Fangshan District First Hospital from August 2019 to August 2020 were randomly divided into control group（n=40，conventional antibiotic treatment）and study group（n=40，antibiotic step-down therapy）. The total effective rate，average hospitalization time，antibiotic use time，fungal colonization rate，mortality rate，lung CT lesion absorption rate and infection control time were compared between the two groups. Results? The total effective rate of the study group was 95.00%，which was higher than that of the control group 75.00%. There was a significant difference between the groups（χ2=6.275，P＜0.05）. The average hospitalization time，antibiotic use time and infection control time of the study group were shorter than those of the control group（P＜0.05）；the incidence of fungal colonization in the study group was 2.50%，and the mortality rate was 2.50%，which were lower than 25.00% and 30.00% of the control group（P ＜0.05）；the lung CT lesion absorption rate in the study group（22.54±4.54）% was higher than that in the control group（14.64±3.42）%（P＜0.05）. Conclusion? The clinical application of antibiotic step-down therapy in patients with severe diabetes pneumonia，can shorten the average length of hospital stay，antibiotic use time，infection control time，and reduce the fatality rate.