Abstract: OBJECTIVE To analyze the relationship between helper T cell 1/helper T cell 2（Th1/Th2）, helper T cell 17/regulatory T cell（Th17/Treg） balance and chronic obstructive pulmonary disease（COPD） combined with lower respiratory tract infection. METHODS The clinical data of 114 patients with COPD in Hainan West Central Hospital from Mar 2018 to Sep 2020 were retrospectively analyzed. Of which, 52 cases were non-infected（non-infection group） and 62 cases were combined with lower respiratory tract infection（infection group）, and 48 people with physical examination were included as healthy control group. The differences in percentages of peripheral blood Th1, Th2, Th17 and Treg were compared among the three groups. Pneumonia Severity Index（PSI） was used to assess the disease severity in infection group, and the relationship between disease severity in infection group and the ratio of Th1/Th2, Th17/Treg was analyzed. RESULTS Th17/Treg of the infection group was significantly higher than that of the non-infection group and the healthy control group（P＜0.05）. Th1/Th2 of the infection group was significantly lower than that of the non-infection group（P＜0.05）, but significantly higher than that of the healthy control group（P＜0.05）. Th1/Th2 of the non-infection group was significantly higher than that of the healthy control group（P＜0.05）. The ratio of Th17/Treg between different disease severity status were compared, and the difference was significant（P＜0.05）. The Th17/Treg ration of grade II was significantly lower than that of grades IV and V（P＜0.05）, and the Th17/Treg ratio of grade III was significantly lower than that of grade V（P＜0.05）. CONCLUSION In COPD patients combined with lower respiratory tract infection, Th1/Th2 balance shifted to Th2, Th17/Treg balance shifted to Th17, and the Th17/Treg ratio increased significantly in severe patients.